If an image is cropped what I'll usually do is Google Image Search because it will usually find the full image as well, even if it doesn't find a high resolution version, then I can search the full size one on IQDB since IQDB doesn't seem to play nice with cropped/altered stuff...
I don't think that's in add-on by default though, so here's the settings if you need to add it...
Left Click Settings
Right Click Settings
GET Var Markers (same)
(left one = no check)
I changed the google image links to Canada's SSL version of the site since the US version is permanently censored.edit:
I changed them back to *.com since now even Canada's is censored.