Here's what it says in the FAQs
Can I post images?
Yes, images can be shown in your posts. If the administrator has allowed attachments, you may be able to upload the image to the board. Otherwise, you must link to an image stored on a publicly accessible web server, e.g.
. You cannot link to pictures stored on your own PC (unless it is a publicly accessible server) nor images stored behind authentication mechanisms, e.g. hotmail or yahoo mailboxes, password protected sites, etc. To display the image use the BBCode tag.
I usually shrink photos on the computer rather than my phone for uploading to forums. Shouldn't make a difference though.