Photo sizes creating blank spaces

Hello, I just started using your plugin, I do love being able to add a gallery for each user but my galleries do not look neatly tiled like the examples in the screenshots you provide.

Depending on the original orientation of the photos (landscape or portrait) there are huge blank spaces between the thumbs.

How can I set the photos to square tiles like in your demo screenshot?

see example of my problem here: http://madmadmakers.com/user/tanyanaser/?profiletab=gallery_photo

Thank you very much for your help.

https://wordpress.org/plugins/ultimate-member-gallery/