Hi! I have the same problem and I've tried to find a solution here in the forum, but it all seems very confusing to me. Some older solutions doesn't work for me at all, I guess it's because I use a newer version...
Well, the problem is this:
I want UNcropped thumbnails with the biggest side set to one value (100), so that I can make them line up nicely on the page. (But most important is that they are UNcropped!)
My settings in the "theme options" are as follows:
(I've tried them all + used "purge cache")
Thumb size: 100
Crop thumbnails: UNchecked, Crop width and Crop height: BLANK
Image size: 595, Longest side
The problem is that they REMAIN cropped.. (as you might have guessed)
I'm using Zenphoto version 1.2.2 with a custom theme based on the default one (light version), but the same behavior appears when i use the unmodified default theme.
A have so far spent a bit too many hours with this problem and i feel that I'm not getting anywhere. I have tried changing the php code according to older posts here in this forum, but as i said it didn't work for me.. If I would be a programmer maybe it wouldn't be so difficult but since I'm just a poor designer I could need some help..
I also understood that i can download a "Nightly build".. but is that the only solution and does it work? ..or is there a way i can modify the php code that is not to complicated.. (with some help)
Another problem is that pictures uploaded with transparent background (like gif or png) get a BLACK background by default in the thumbnail. Is it possible to change this setting to WHITE by default?
I'm very thankful if anyone could give me some advice on this, or at least link to another post that can be helpful that I might have missed.
Btw, very nice job with the gallery it's the best one I've tried, love it!

(except for this bug of course..)

Next step is trying out Zenpages, it looks like a very good application too..