直接連結

直接連結與HTTP

在全球資訊網幕後的超文字傳輸協定（HTTP）技術中，並未對鏈路類型做任何區分，所有連結的功能均為平等，資源可以位於任何伺服器的任何位置。
當存取一個網站時，瀏覽器首先下載HTML格式的文件內容。下載的HTML文件可能呼叫其他HTML檔案、圖像、指令碼及樣式表等檔案。這些檔案可以包含<img>標籤以在頁面上顯示所提供URL位置的圖像。其中的HTML代碼可能不指定伺服器，從而使網頁瀏覽器使用與父代碼（<img src="picture.jpg" />）相同的伺服器。但它也可以指定在某個伺服器上代管的圖像的絕對URL，例如(<img src="http://www.example.com/picture.jpg" />。
在瀏覽器下載到包含圖像的HTML圖像後，瀏覽器將聯繫遠端伺服器以請求圖像內容。

用戶端側

大多數網頁瀏覽器都將直接根據網頁指示來取得圖像。 嵌入式圖像可能以此作為一個網路信標來跟蹤用戶或將資訊傳遞給第三方。有許多廣告過濾工具可不同程度地限制此類行為。

伺服器側

部分伺服器採用HTTP參照位址等技術檢測直接連結，並可根據相同格式返回錯誤、告知、啟動或譴責資訊，代替原始的目標圖像。大多數伺服器都可配置為避免為第三方直接連結提供代管的媒體內容。
URL重寫（例如Apache HTTP Server的mod_rewrite）經常被用於拒絕或重新導向直接連結的圖像或媒體內容到其他資源。大多數媒體資源都可通過此種方式重新導向，包括影片檔、音訊檔案、動畫資源（例如Flash）等。
Other solutions usually combine URL重寫 with some custom complex 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 third party website.

直接連結引起的版權法律問題

The most significant legal fact about inline linking, relative to copyright law considerations, is that the inline linker does not place a copy of the image file on its own Internet server. Rather, the inline linker places a pointer on its Internet server that points to the server on which the proprietor of the image has placed the image file. This pointer causes a user's browser to jump to the proprietor's server and fetch the image file to the user's computer. US courts have considered this a decisive fact in copyright analysis. Thus, in 完美十訴亞馬遜案, the 美國聯邦第九巡迴上訴法院 explained why inline linking did not violate US copyright law:
Google does not...display a copy of full-size infringing photographic images for purposes of the Copyright Act when Google frames in-line linked images that appear on a user’s computer screen. Because Google’s computers do not store the photographic images, Google does not have a copy of the images for purposes of the Copyright Act. In other words, Google does not have any 「material objects...in which a work is fixed...and from which the work can be perceived, reproduced, or otherwise communicated」 and thus cannot communicate a copy. Instead of communicating a copy of the image, Google provides HTML instructions that direct a user’s browser to a website publisher’s computer that stores the full-size photographic image. Providing these HTML instructions is not equivalent to showing a copy. First, the HTML instructions are lines of text, not a photographic image. Second, HTML instructions do not themselves cause infringing images to appear on the user’s computer screen. The HTML merely gives the address of the image to the user’s browser. The browser then interacts with the computer that stores the infringing image. It is this interaction that causes an infringing image to appear on the user’s computer screen. Google may facilitate the user’s access to infringing images. However, such assistance raised only contributory liability issues and does not constitute direct infringement of the copyright owner’s display rights. ...While in-line linking and framing may cause some computer users to believe they are viewing a single Google webpage, the Copyright Act...does not protect a copyright holder against [such] acts....