An online digital photo forensics tool like FotoForensics.com uses Error Level Analysis (ELA) to discover the error level differences on a photograph that was saved using a lossy compression algorithm, like JPEG. ELA algorithm enables us to determine if a photo was digitally modified. Similar surfaces and similar edges should appear similar under ELA. If not, it might indicate a digital manipulation.
Flat-Earthers like to use ELA to ‘prove’ a photo has been tampered with. It occurs because they do not understand how ELA works. Most of them appear to assume if the picture is an original, it would show a uniform ELA. Using such a digital forensic ‘skill’, we can actually ‘prove’ all digital photos as fake.