This plugin is just great - exactly what I was looking for, thanks!
Unfortunately, it shows way too few results comparing to other sources. For example, I was looking for photos about "Schweizerisches Landesmuseum". The plugin showed only 3 photos. Repeating the search only for "Schweizerisches", it found 9 pics.
Searching the same term on http://photopin.com/search/schweizerisches-landesmuseum gave 28 results (including the 3).
The same search on Flickr (http://www.flickr.com/search/?q=schweizerisches+landesmuseum&l=cc&ct=0&mt=all&adv=1) also returned 28 results.
Looking on the code, I saw that you are only searching for license 4 & 7. This is very limiting. Could you put the licensing option directly in the search form or display it along with the images?