What determines the crop used for group photos?

In the Group View page there is a group photos block that works best when it's in the widest column, however, it takes up a lot of page real-estate and we've got it in a side narrow column position. However, when you select a photo only the middle portion is displayed instead of making the whole image smaller in proportion. Any ideas where to start with changing this display to proportionate rather than showing a small portion of the full-size image?

It works with real sizes of images. So you need to change image sizes in photos module to make images smaller, but it will not affcet old images and will ally to any newly uploaded images which rely on photos module.

Another solution is to replace image gallery with some another gallery, but it requires custom programming in template files.

Thanks AlexT, I'll look into the options. Thanks for the starting point.