[butterdezillion]

So if I scanned a document without editing it in any way, saved it as a jpeg or pdf, and posted it to my blog, could somebody who doubted its genuineness use MD5 to find that it has not been manipulated or edited in any way?

Of course, if I got a PDF from somebody else and they edited it in any way that would show, right?

[Rightwing Conspiratr1]

So if I scanned a document without editing it in any way, saved it as a jpeg or pdf, and posted it to my blog, could somebody who doubted its genuineness use MD5 to find that it has not been manipulated or edited in any way?

No.

Of course, if I got a PDF from somebody else and they edited it in any way that would show, right?

No, unless you were the one who scanned the original PDF.

[E. Pluribus Unum]

The genuineness of the original document has nothing to do with the checksum.

You can perform a checksum on your original scanned file and post the image and the checksum on your site.

A person who downloaded the file could run a checksum on it. If his checksum matches the sum you posted, he has a genuine, unaltered copy of your file.

If the checksums differ, the files are not identical.

[bvw]

There’s no perfect way to be sure. MD5 keys can be duped with a different set, in cases even one that might pass as a dup image. It’s expensive and takes a lot of work or infrastructure, so it’s highly unlikely.

Nothing beats personal and a society’s regard for honesty and integrity and there is, in the end, no techno substitute.