Portfolio items not displaying same size

Hi, beautiful theme!

Here’s a link so you can see what’s going on: http://orange-county-graphic-design.com/portfolio/

I created all my portfolio images in the same size (575×700). Each image displays fine on its dedicated page. But the main Portfolio page displays some of the images with the bottom section cut off. I can’t for the life of me figure out what I’m doing wrong, because it seems all my configurations are the same from one post to the other. What did I miss?