PhotoSearch is described as 'Search Photos for hashtags and users. Browse and explore public Images'. There are more than 10 alternatives to PhotoSearch for a variety of platforms, including Online / Web-based, Mac, Firefox, Opera and Google Chrome. 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 apps like PhotoSearch are Search by Image (Free, Open Source), SauceNAO (Free), Yandex.Images (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.