TinEye
There are plugins for various browsers!
http://www.tineye.com

Google Advanced Image Search
Fill in the "width" and "height" fields, then enter a keyword related to the image.

But these methods don't always work.
Any other ideas?

Ask on furry imageboards like tgfb or lulz.net, or an IRC channel populated by knowledgeable furries. Also this would be useful for artwork in a japanese style.

http://www.furaffinity.net/search/

It is very limited in terms of quality (it depends how the artist tagged or described their art) and quantity (can only return 60 result at a time, and will often crash if you input over 3 words), it however often works to find pokemon stuff.

Keep in mind the pictures on furaffinity will NOT appear in google searches (unless they changed it).

http://www.deviantart.com/

It let you search resolution in format widthXheight.

Also note e621 used to be the best archive to keep track of the artists' different aliases and galleries, see what i said months ago : forum #8427.
None ever answered my remarks, heh.