Is this question about a specific task on this site, secure.phabricator.com, or some other site? Your question does not contain enough details to give you an answer.

In the general case, you remove images by editing the text area and removing the file reference {F12345}.

Yes, from this site. If you click here Abuse and search for task T7593, you see there is an image attached to the ticket in the Workboard. If you edit the ticket, you don't find something like {Fxxxx}.

Drag a different photo on top of it.

T10293

But I don't want a new photo. I want to remove the photo.

Did you try reading the task I linked above?

ooh, sorry. I believed that the linked task is an example. Ok, there is a ticket for it. Subscribed.