Not enough information given in your question.
Do you have a situation where more than one photo is attached and one of them does not belong with the other stone(s)? This happens often when the link button is not pressed at the right time.
If that is the case you can unlink the image and send it back to the transcription queue and if it has been transcribed, you can "erase" that transcription by replacing the information with a duplicate version of a wanted record. This is called a "fake merge". After you have created the dummy duplicate, click on the original and when it opens in record screen will see a white up-arrow in the blue top bar. Click that and you merge the two records into one.
If that is not what you need/want to do, reply back here wih more details, and include the URL of the record you have in mind.
If you want a photo removed completely from the BG site, you have to send a specific request to BG support at the link on the dashboard/bottom of the page.