Once you start a thread, you can't delete it from your end - at least I don't think so. Administrators will need to do that. So if you need to remove a pic or comments, just "Edit" that post and remove whatever you don't want. You can also enter something like, "Delete Post" or "Entered in Error" for someone else to see later if you want it removed totally.
As for adding pics, have you tried linking your photos from Photobucket? That's what many of us do here on TFP. Upload your pics to Photobucket (free), then copy & paste the IMG code for that pic from Photobucket to your TFP post. Works great.
Also, you can try going to the bottom of your quick reply post where it says “Go Advanced”, and then down to where it says “Manage Attachments”. It may let you upload them that way. They may show-up large because you can't adjust the size of the attachment, but it may work.