- System Restore doesn't modify your data, only the operating system - by design. (Would you want it modifying your files? I wouldn't!)
- Assuming the standard resolution of 300dpi, a 32"x24" JPEG will be a lot bigger than 2.4kB. More like 2.4MB, possibly much larger, depending on the quality. They would be in the range that some ISPs consider "too big", so that part I can understand. My camera is "only" 6 megapixels but each photo is about 1MB in JPEG, ad 10MB in RAW format. What camera was it, or were the photos scanned?
- I don't know of any mechanism that would cause your files to expand in size by themselves. I have to say that the most likely explanation is you: something you did, or (more likely) the photos are fine, and picture files really can get that big, straight from the camera or scanner.