The forum has a pretty strict file size limit. I've tried posting PDF's, but I can never get the file size under the limit no matter how much I cut out and compact.
So if you get an error, try checking the size of the photo.
You might have better luck uploading to a photo storage site like photobucket, and then creating a link to that photo. But I think any photos uploaded to photobucket are accessible to anyone, so don't upload personal stuff to that site.
The management attachment on the forum has a lot to be desired. I would upload to a free hosting site such as, Photobucket, shutterfly, Picassa, etc and then left click on the image and copy the url. Then paste it in the dialog box that appears when you select the icon from above. The icon is n the middle row in the 4th group from the left-- it is the 3rd icon.Look for the "Manage Attachments" button below the box into which you type your comments.