C64 disk image FTP or search of .scp images

[jupp]

Then you have valid data in the image and on the backup also. It's really as simple as that.

but only because it is valid MFM/GCR/FM/whatever it is in no way guaranteed that it is the correct data. the only way to find that out is to decode it and compare against known good data. or to word it in a different way: if the GCR is invalid, then you know that it is incorrect data. but the other way around is not guaranteed.