A. In the film era, it was very difficult to make changes to most non-“light”-related aspects of photographs without viewers noticing.

It would often take an expert significant time to make those changes — and even then the changes were usually detectable upon examination of the print or negative (as opposed to published versions of doctored photos, where the low quality of the printing often obscured the manipulations).

People back in the film era usually called those doctored images “retouched” or “airbrushed.”

B. But now, in the digital age, it’s easy for anyone to make non-“light”-related changes, quickly and undetectably, with the swipe of a finger on their smartphone.

Things within a photo can be selectively replaced, moved, blurred, added, deleted, reshaped, and resized — all without viewers of the image having any clue.

“B” explains one of the main reasons the public is more skeptical of any images that look like photographs now than they were even 20 years ago:

Viewers have learned how easy it is in the digital age to undetectably alter things that viewers know “wouldn’t change unless someone intervened to change them” — that is, “forms and shapes.” (See also #2 in this brief.)