Yandex.Images is described as 'search for images on the internet, search by image'. There are more than 10 alternatives to Yandex.Images, not only websites but also apps for a variety of platforms, including Google Chrome, Mac, Firefox and Opera. The best alternative is TinEye. It's not free, so if you're looking for a free alternative, you could try Google Images or Image Search Options. Other great sites and apps similar to Yandex.Images are NooBox (Free, Open Source), Search by Image (Free, Open Source), SauceNAO (Free) and Qwant Images (Free).
Search by Image is a Firefox extension which enables you to initiate a reverse image search from the right-click context menu or the browser toolbar, and comes with support for more than 30 search engines.
SauceNAO is a reverse image search engine. The name 'SauceNAO' is derived from a slang form of "Need to know the source of this Now!" which has found common usage on image boards and other similar sites.