It’s interesting you call it hearsay, because this would neatly fit into some of the exceptions to the rules AGAINST hearsay:

Records of a Regularly Conducted Activity. A record of an act, event, condition, opinion, or diagnosis if:

(A) the record was made at or near the time by — or from information transmitted by — someone with knowledge;

(B) the record was kept in the course of a regularly conducted activity of a business, organization, occupation, or calling, whether or not for profit;

(C) making the record was a regular practice of that activity;

(D) all these conditions are shown by the testimony of the custodian or another qualified witness, or by a certification that complies with Rule 902(11) or (12) or with a statute permitting certification; and

(E) the opponent does not show that the source of information or the method or circumstances of preparation indicate a lack of trustworthiness.

If it was a high-profile case and the screenshot was evidence of a crime, I’m assuming they have people that could weigh in as an expert on doctoring images?

How would you differentiate between a screenshot of an email in gmail and a screenshot of an email in gmail where someone had inspected the source and changed the text before screenshotting?

Good point. If it was the only evidence and didn’t connect with anything else it would not be substantial proof. I would think it could add to a story but not be definitive proof? You are describing the defense against the screenshot which could be backed up by “expert” testimony. Here is something I found on e-mails being edited in outlook even: https://community.spiceworks.com/topic/1135234-can-i-protect... (questionable source)