Pete,
After you copy (ensure you use the second option from the bottom that indicates "for Forums" try using the alternate paste technique, ie: put your cursor where you want the photo in your post, then hold down your Control Key ("Ctrl" on your keyboard) and tap the "V" key. Release the keys and your Photo's link description should be in place. I am, I assure you, a mere toddler when it comes to computer skills so this explanation might be a bit hard to follow I know! Hope it's of some help.
Cheers,
Lance