science

Inline linking

Inline linking is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Inline linking rather than just read about it. In short: Inline linking (also known as hotlinking, piggy-backing, direct linking, offsite image grabs, bandwidth theft, or leeching) is the practice of using or embedding a linked object—often an image—from one website onto a webpage of another website. In this process, the second site does not host the object itself but instead loads it directly from the original source, creating an inline link to the hosting site.

Key takeaways

Inline linking belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Inline linking to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Inline linking from memory before moving on to harder problems.

Reference excerpt

Inline linking (also known as hotlinking, piggy-backing, direct linking, offsite image grabs, bandwidth theft, or leeching) is the practice of using or embedding a linked object—often an image—from one website onto a webpage of another website. In this process, the second site does not host the object itself but instead loads it directly from the original source, creating an inline link to the hosting site.

HTTP and inline linking The Hypertext Transfer Protocol (HTTP), the technology behind the World Wide Web, does not differentiate between different types of links—all links are functionally equal. As a result, resources can be linked from any server and loaded onto a web page regardless of their original location. When a website is visited, the browser first downloads the HTML document containing the web page's textual content. This document may reference additional resources, including other HTML files, images, scripts, or stylesheet. Within the HTML, <img> tags specify the URLs of images to be displayed on the page. If the <img> tag does not specify a server, the web browser assumes that the image is hosted on the same server as the parent page (e.g., <img src="picture.jpg" />). If the <img> tag contains an absolute URL, the browser retrieves the image from an external server (e.g., <img src="http://www.example.com/picture.jpg" />). When a browser downloads an HTML page containing such an image, the browser will contact the remote server to request the image content.

Common uses The ability to display content from one site within another is part of the original design of the Web's hypertext medium. Common uses include:

Avoiding copyright infringement: it is copyright infringement to make copies of a work for which the person making copies has no license, but there is no infringement when the re-user provides a simple text link within an HTML document that points to the location of the original image or file (simply called a "link"). Web architects may deliberately segregate the images of a site on one server or a group of servers. Hosting images on separate servers allows the site to divide the bandwidth requirements between servers. As an example, the high-volume site Slashdot stores its "front page" at slashdot.org, individual stories on servers such as games.slashdot.org or it.slashdot.org, and serves images for each host from images.slashdot.org. An article on one site may choose to refer to copyrighted images or content on another site via inline linking, which may avoid rights and ownership issues that copying the original files could raise. However, this practice is generally discouraged due to resulting bandwidth loading of the source, and the source provider is often offended because the viewer is not seeing the whole original page, which provides the intended context of the image. Many web pages include banner ads. Banner ads are images hosted by a company that acts as middleman between the advertisers and the websites on which the ads appear. The <img> tag may specify a URL to a CGI script on the ad server, including a string uniquely identifying the site producing the traffic, and possibly other information about the person viewing the ad, previously collected and associated with a cookie. The CGI script determines which image to send in response to the request. Some websites hotlink from a faster server to increase client loading speed. Hit counters or Web counters show how many times a page has been loaded. Several companies provide hit counters that are maintained off site and displayed with an inline link.

Controversial uses The blurring of boundaries between sites can lead to other problems when the site violates users' expectations. Other times, inline linking can be done for malicious purposes.

Content sites where the object is stored and from which it is retrieved may not like the new placement. Inline linking to an image stored on another site increases the bandwidth use of that site even though the site is not being viewed as intended. The complaint may be the loss of ad revenue or changing the perceived meaning through an unapproved context. Cross-site scripting and phishing attacks may include inline links to a legitimate site to gain the confidence of a victim. Pay-per-content services may attempt to restrict access to their content through complex scripting and inline linking techniques. Inline objects can be used to perform drive-by attacks on the client, exploiting faults in the code that interprets the objects. When an object is stored on an external server, the referring site has no control over if and when an originally beneficial object's content is replaced by malicious content. The requests for inline objects usually contain the referrer information. This leaks information about the browsed pages to the servers hosting the objects (see web visitor tracking).

Prevention

Client side Most web browsers will blindly follow the URL for inline links, even though it is a frequent security complaint. Embedded images may be used as a web bug to track users or to relay information to a third party. Many ad filtering browser tools will restrict this behavior to varying degrees.

Server side Some servers are programmed to use the HTTP referer header to detect hotlinking and return a condemnatory message, commonly in the same format, in place of the expected image or media clip. Most servers can be configured to partially protect hosted media from inline linking, usually by not serving the media or by serving a different file. URL rewriting is often used (e.g., mod_rewrite with Apache HTTP Server) to reject or redirect attempted hotlinks to images and media to an alternative resource. Most types of electronic media can be redirected this way, including video files, music files, and animations (such as Flash). Other solutions usually combine URL rewriting with some custom server side scripting to allow hotlinking for a short time, or in more complex setups, to allow the hotlinking but return an alternative image with reduced quality and size and thus reduce the bandwidth load when requested from a remote server. All hotlink prevention measures risk deteriorating the user experience on the third-party website.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Inline linking

Start with the simplest possible case. Write down what Inline linking claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Inline linking before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Inline linking ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Inline linking

In research: Inline linking appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Inline linking in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Inline linking is common in secondary-school and first-year university syllabi. It links to neighbouring topics File sharing, Hypertext, Internet ethics, so understanding it makes those chapters shorter.
In everyday life: Look for Inline linking outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Inline linking in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Inline linking means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Inline linking out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Inline linking in simple terms?

Why does Inline linking matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Inline linking?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Inline linking.