Why are my pictures like this????

I used to have a Dell laptop before getting a MacBook Pro. When I took it into my college's computuer store to be fixed one time, I received it back with all my photos on the harddrive ruined. The pictures themselves were not distorted but portions of the photo had different hues (ex., one half would be normal and then another half had a yellow hue). The lines marking the two parts could go in any direction and any hue color has happened. The store told me unfortunately there was nothing I could do. Even the thumbnails of the photos were showing this problem.

However, when I transferred all my photos over to my MacBook Pro, I realized that although the color distortions were still there, the thumbnails were perfectly fine and not indication there was a problem. Is there any way to restore my photos from the thumbnail image, and why are they like this in the first place?!?!?!?

Thank you!