I have just copied a picture from the internet, and I have successfully pasted it on an email message and sent it. This is what I did:
1. open email 'compose' page, so that I didn't have to faff about when I had the picture ready and waiting.
2. right-click on picture.
3. on drop-down menu, left-click on 'copy'.
4. call up email 'compose' page.
5. press and hold Ctrl key, then press V.
6. picture appears on email 'compose' page.
7. click 'Send' and picture is sent.