I am no good with Mac. Here is step by step how I put a photo in.

1. At the bottom of your message box, there is a small place to make "attach image(s)". Mark it

2. You can then hit the browse button and browse images one at a time.

3. When you are done, go below and simply hit SUBMIT. I tried preview but it messed it all up for me.

Remember, you can always edit after your post hits.