Reverse Image Search EnginesEdit
IQDB - *booru board searcher. Use it for anime images. It's probably gonna be the first thing you should use for source. Also has a 3D option.
SauceNAO - Pixiv image searcher. It's your second option if IQDB doesn't work out well. It also has a few anime screenshots.
TinEye - General image searcher. Shit sucks.
Google - Drag-and-drop, keyword-entering magic. Turn to this if the others fail.
Doujin/Hentai Portals like doujinshi.mugimugi.org and g.e-hentai.org support file search, as seen in the right picture. Some of the board archives also support searching for posts with the same image hash. And remember, looking at the filename, recognizing artist/studio styles, and knowing the current airing season will really help you not look stupid.
Image Search Options is pretty nifty for reverse image searching too.
Overbooru - Huge list of *boorus
Danbooru (anime artwork) - The "original" *booru. A lot of *boorus scrape from here.
Konachan (anime wallpapers)
yande.re (high-res scans) - Used to be oreno.imouto.org.
Gelbooru (anime artwork)
Sankaku Channel (anime/manga/game images)
e-shuushuu (anime/manga/game images)
The Anime Gallery (anime images & wallpapers)
Zerochan (anime images & wallpapers)
Manga Drawing (anime/manga/game images)
Nekobooru (anime/manga/game images)
Wallbase - Wallpapers. A lot of anime ones in there too.
4walled - Wallpaper board scrapper. Board /w/ for anime.
Anime Paper - High quality wallpapers, vectors, and other anime pictures.
AnimeWP - Anime wallpapers, I guess.
2ndRarfag - Enjoy.