Yes, There must be a better way.
The existing method to delete a picture ; One at a time , look at the thumbnail pic, click to open, click to delete, click to confirm, is tedious but do-able.
However when there are several pictures to delete, it would be good to be able to select multiple discards and then go through a delete process.
Pehaps an 'are you really sure" process, then the pics are removed from the group page.
Perhaps keep the discards somewhere else for a while, a day, to allow inspection and change of mind, after which the pics are deleted permanently.