I'm using "Zenphoto version 1.4.1 [7551]" with the default theme, and I'm having difficulties in configuring the "crop thumbnail options".
From what I understand, it should start by cutting out some margins from the top and bottom and left and right before rescaling the image.
However it seems that it only does that on the largest "direction" of the image !?! ie: if the image's width is larger than its height, the crop will be done as expected from the left and right sides, but only from the bottom side (and nothing is cut out from the top!).
An example of that on the following album:
http://www.tibonihoo.net/photos/melbourne/The crop thumbnails's parameters used there are: 16% left & right, 16% top & bottom (a bit too large but the problem arises with smaller percentages).
Zenphoto
