I can't see any photos, just empty frames with X's inside? What gives?

This problem be caused by running Zone Alarm or Ad-Blocker in the background.

If you’re running Zone Alarm here’s how to get it to be friends with Photocase:

1. Double click Zone Alarm

2. Click on the left where it says "privacy"

3. In the "Sites" column you will already see Photocase.com. You will have to allow all options there.

Then right-click your mouse button on "Photocase.com" > "preferences" > "ad blocker" > "block ads" and unselect all.

Thanks to Smartinka for the hint.