First upload your photo with the photobucket app
Once the photo has been uploaded tap on the "share" icon that in this photo is the second from the left on the bottom.
Now choose the "copy link to clipboard"
Choose the "HTML" link
Type your message first then hold down on the screen to bring up your copy and paste options. Tap the clipboard icon that in this pic is the one on the top far right.
Last but not least post your discussion.. Good luck