Elog.io is a good example of an open source and free software. The products itself is a tool set for web researches. It integrates with the browser and then, when the images are detected on a page, identifies images in the Elog.io database to find attribution information.
Basically, it allows users to easily find an answer to the question: is this photograph I'm looking at openly licensed? If no, who holds the copyright? They can also copy a photograph and its attribution easily into programs like Wordpress, LibreOffice and Word. The solution is based on advanced perceptive hash algorithm to find visually similar images even if they were colored, resized or cropped. Currently, the database includes over 22 million images from Wikimedia Commons. The image matching algorithm understands basic things like resizing and color change.
Logicify set up a team of a single person and technical advisory access to accomplish this project. The developer had to analyze a large sample of possible website designs and do extensive testing of the resulting extension to make sure the injected script would not interact with the target websites currently opened in a tab. The extension was written specifically for Google Chrome. The algorithm for calculating matches was developed on the server side. Our goal was to work reliably with the heterogeneous world of web pages to locate images perfectly. The images found in the DOM were hashed , so the algorithm had to be carefully tuned to meet memory and processor limitation of the typical commodity hardware. The product was completed and released into Google Chrome store.
- Back-end: Node.js