Help! My jpeg files are turning into Unix Executable files!

I removed the hard drive of my old Mac G5 so I could recycle the computer, but save the files on the hard drive. I hooked it up to a Universal Drive Adaptor and connected it to my Mac OS X. I can view most things. While looking at wonderful photos from many years ago, I did one simple thing: some of them were sideways, so I simply rotated them. Next thing I know, every jpeg that I rotated had been converted to a "Unix Executable File" and the photo is gone! Where the thumbnail of the photo should be, there is only a gray tile. When I click on the tile, I simply get this Unix Executable File text. When I right click on the tile and then click on Get Info, a column appears that still shows the photo thumbnail. Also, when I click on "Quick Look," I can see the photo, but it is not accessible. I have taken a screen shot of all of these steps:

I would be so very, very grateful if anyone can help me to A) convert the file back into a jpeg (or some similar file) and B) tell me how I can avoid letting this happen again. I can easily imagine someone else at some point looking at these photos and wanting to rotate them right side up, only to end up in this same unhappy situation.

Thank you very much,

Steph