This is one of the dumber arguments revisionists use. You can't prove a negative. You cannot prove they were NOT photoshopped. The onus is on the accuser to prove they WERE photoshopped, and the reason they can't prove that is because 1) they weren't, 2) they existed long before photorealistic Photoshop techniques that could create such a convincing fake, and 3) they are corroborated by first hand accounts of photographers, victims, and perpetrators. There are few things in history with as much corroborating evidence as the single largest, coordinated effort to exterminate a culture in human history. Anyone who refuses to believe all the evidence, ranging from bank records and official reports to personal journals and autopsies of corpses found in mass graves, is not arguing in good faith, or trying to determine historic fact. Rather, they are trying to confirm a convenient narrative that reinforces their own hilariously evil or misguided beliefs. Present the evidence and leave it at that.