Images resizing (Ess Grid and Featured)

Hello,

I have had this problem in the past, but no one could ever explain what is causing the problem. Somehow, somewhere featured images are being resized and cropped. They are not being shown full height on blog posts, and all of my Ess Grid images are not filling their containers.

When I switched to a default theme, the problem went away. There are also no plugins that seem to be causing the problem, nor is there any custom css that is affecting it. Please please help, this is causing a lot of embarrassment since grids and images are so crucial to my site. Again, this problem DOES NOT CONTINUE if I switch themes.

Here is the example of a posts featured image not displaying right:
http://www.parpreschurch.com/summer-picnic-congregational-photo/

Here is an example of an Ess Grid that is not displaying correctly:
http://www.parpreschurch.com/summer2015/

Screenshot shows how the grid as a whole is fine, and the cover is correct, but the images are not filling their containers. They seem to be scaling by height.