/r/Anime - Reddit
https://www.reddit.com/r/anime/wiki/reverse_image_searching/
WEBSauceNAO: Probably the best site by far if you are looking for the artist for fan art. It searches Pixiv and Nico Nico Seiga, among other sites. Generally will get you a direct link to the work and artist, and for official art it will list the artist, series, and characters.
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