I am unable to view my pictures on my Macbook Pro saved on an external that were put there using windows software. I keep getting this message: "It may be damaged or use a file format that Preview doesn’t recognize."
What happens if you copy a few to your local drive? Same thing? If not, seems like the format of the external drive may be causing some problem. The solution might be to copy them to your HDD, format the external in a Mac compatible and copy them back.
The drive is probably formatted as NTFS (commonly used in the Windows world) but that shouldn't stop the Mac from reading the files assuming the files were written properly.
Copying a few of the files to the Mac drive is worth a try but I suspect won't help much if any. If it doesn't put the external drive back on that Windows machine and attempt to read the files. Also wouldn't hurt to have Windows test that external drive and make sure the file structure is intact.