I am looking to delete a photo sent by my bot (reply_photo()), I can't find any specific reference to doing so in the documentation, and have tried delete_message(), but don't know how to delete a photo. Is it currently possible?
You need to have the chat_id and the message_id of that message sent by bot, then you can delete using context.bot.delete_message(chat_id, message_id).
Note: Bot cannot delete a message if it was sent more than 48 hours ago.
Telegram Bot delete sent photos?