What is happening to image files I download? They show up as blanks. Any ideas?

I found a website that had old (out of copyright) images from old books, prints, etc. I like to keep old illustrations simply because I enjoy them so much. So, on this website, there were quite a few images. I “Saved the Image” on to my computer and it registered as a gif. When I went to open up the files to look at them again, they were just blank. This happened on all of the ones from this site (not others). The name of the files were there, and just a big square blank. My files are being saved on a program called “Serif” (basic) but I have had no problems with saving illustrations off other sites. Is it that it is a “gif” and that’s why it doesn’t show up? What can I do to copy these illustrations onto my computer? Am I not saving them properly? Is there a block that this site has? It shouldn’t have one as the illustrations are in the public domain now. Any ideas on what to do?

Thank you very much!