Thanks, Anton. That was helpful. I've experimented some more, discovered where to turn the camera round and found that when I take a photo actually in messages, it seems to send automatically. Backspacing didn't do anything. This function may be useful on occasion but I find it more satisfactory to take a photo first and then select, (having deleted the bad ones) - which brings up the option to choose or cancel.
What you said about deleting individual messages was very useful, indeed - once I found the trash icon had appeared.
Speaking of which you may be able to answer another query. In my personal/business email accounts, I have the option (via bin icon) to trash anything I don't want to keep but in my gmail account I can only trash things if I access it on the computer. Is there any means of doing it on the phone?