Google Images

Google Images is a search service owned by Google that allows users to search the World Wide Web for image content.[1] It was introduced on July 12, 2001 due to a demand for pictures of Jennifer Lopez's green Versace dress that the regular Google search couldn't handle.[2][3] In 2011, reverse image search functionality was added.

When searching for an image, a thumbnail of each matching image is displayed. When the user clicks on a thumbnail, the image is displayed in a larger size, and users may visit the page on which the image is used.

Beginnings and expansion (2001–2011)
In 2000, Google Search results had been limited to simple pages of text with links. Google's developers worked on developing this further, and they realized that an image search tool was required to answer "the most popular search query" they had seen to date: Jennifer Lopez in her exotic green Versace dress. As a result of this, Google Image Search was launched.[4] By 2001, 250 million images were indexed in Image Search. This number would eventually grow to 1 billion images by 2005 and 10 billion by 2010.[5]

In early 2007, Google implemented an updated interface for the image search, where information about an image, such as resolution and URL, was hidden until the user moved the mouse over its thumbnail.[6] This was discontinued after a few weeks.

On October 27, 2009, Google Images added a feature to its image search that can be used to find similar images.[7]

On July 20, 2010, Google made another update to the interface of Google Images, which reimplemented the hiding of image details until mouse over.[8]

In May 2011, Google introduced a sort by subject feature for a visual category scheme overview of a search query.[9]

A month later, in June 2011, Google Images added a Search by Image feature which allowed for reverse image searches directly in the image search-bar without third-party add-ons. This feature allows users to search for an image by dragging and dropping one onto the search bar, uploading one, or copy-pasting a URL that points to an image into the search bar.[10]

New algorithm and accusations of censorship (2012–present)
On December 11, 2012, Google Images' search engine algorithm was changed once again, in the hopes of preventing pornographic images from appearing when non-pornographic search terms were used.[11][12][13] According to Google, pornographic images would still appear as long as the term searched for was specifically pornographic; otherwise, they would not appear. While Google stated explicitly that they were "not censoring any adult content", it was immediately noted that even when entering terms such as "blow job", or "boob," no explicit results were shown.[13][14] The only alternative option was to turn on an even stricter filter which would refuse to search for the aforementioned terms whatsoever.[14] It was also noted that users could no longer exclude keywords from their search as before.[15]

On February 15, 2018, Google Images' interface was modified in order to meet the terms of a settlement and licensing partnership with Getty Images. The "View image" button (a deep link to the image itself on its source server) was removed from image thumbnails. This change is intended to discourage users from directly viewing the full-sized image (although doing so using a browser's context menu on the embedded thumbnail is not frustrated), and encourage them to view the image in its appropriate context (which may also include attribution and copyright information) on its respective web page. The "Search by image" button has also been downplayed, as reverse image search can be used to find higher-resolution copies of copyrighted images. Google also agreed to make the copyright disclaimer within the interface more prominent.[16]

Search by Image feature
The Search by Image feature in use

Google Images has a Search by Image feature for performing reverse image searches. Unlike traditional image retrieval, this feature removes the need to type in keywords and terms into the Google search box. Instead, users search by submitting an image as their query.[10] Results may include similar images, web results, pages with the image, and different resolutions of the image.

The precision of Search by Image's results is higher if the search image is more popular.[17] Additionally, Google Search by Image will offer a "best guess for this image" based on the descriptive metadata of the results.

Algorithm
The general steps that Search by Image takes to get from a submitted image to returned search results are as follows:[18]
 * 1) Analyze image: The submitted image is analyzed to find identifiers such as colors, points, lines, and textures.
 * 2) Generate query: These distinct features of the image are used to generate a search query.
 * 3) Match image: The query is matched against the images in Google's back end.
 * 4) Return results: Google's search and match algorithms return matching and visually similar images as results to the user.