A JPEG is a compression file, but exactly what does that mean, and what exactly are "thumbs?"
A few years ago, before most computers became so powerful, a lot of companies sold file compression software. I had one, and I could compress little used files to a fraction of what they were, and if later I needed that file, or part of it, I could decompress the files to their original size.
Is JPEG compression similar to that, and are "thumbs" the compressed information, or at least a portion of it, that was originally recorded by a camera's sensor? And, when expanding a compressed JPEG by converting it to a much larger TIFF file, does the software expand upon the original information (thumbs) to decompress files similar to what those old file compression programs did with word files and such?