Hope this helps...
At a high level...
Have your pic saved on your local drive (or somewhere you can navigate to)
(note size limits in browse window)
scroll down on the Quick Reply screen to Go Advanced
then scroll down to manage attachments,
and browse to pick and upload your pics...
as shown below (I hope )
Ours: '11 Monaco Diplomat 43DFT followed closely by '14 Jeep 4 dr Wrangler.
Hers: '13 Explorer Sport - AWD 365hp twin turbo scooter!
Previous: '13 Ford F350 CC Platinum and '13 38GK