What is IQDB?
IQDB (Image Query Database) is a reverse image search engine for finding sources of images and identifying duplicates across the web. Developed and released in 2008 by pennywise, IQDB utilizes advanced perceptual algorithms for matching images based on their visual similarity, rather than relying on filenames, metadata or other tags.
An open source software, IQDB has a large and rapidly growing index of over 450 million image hashes. When a user uploads an image or URL to IQDB, it generates a perceptual hash of the image and compares it against pre-computed hashes in its database to find visually similar images. Even if an image has been edited, resized, cropped, recompressed or modified in any way, IQDB is often able to match it to versions available elsewhere.
In addition to giving reverse image search capabilities to end users, IQDB also offers an API that developers can leverage in their own applications. Many popular services like Danbooru and e621 are among the sites that build on top of IQDB's image searching and matching functionalities.
As more images are added to its index through user submissions and web crawls, IQDB continues to enhance its capabilities as a reverse image search engine. With its focus on visual similarity and its open source nature, IQDB fills an important niche among alternatives to provide image matching, searching and saucing capabilities to users across the internet.
TinEye, RevIMG, SauceNAO, Search by Image, trace.moe, GazoPa, Byo Image Search lab, THINK FR33 Reverse Image Search, NooBox, Reverse.photos, Picitup, Safe Design, isk-daemon, Plaghunter, Bingle Goggles, Unravl are some alternatives to IQDB.