Hi Ross,
You may be trying to upload an attachment directly. You may add your photo this way but you do have to deal with more strict image sizes.
It is often simpler to just upload the image to your photo gallery and link from there. After the image is uploaded to your photo gallery you will want to click on the thumbnail of the image.
Below the thumbnails you should now see a medium sized version of your image with two sets of links. Simply copy the "Direct Link" and paste it into you post using the little yellow mountain icon like this.
If you don't use the mountain icon it will not show directly in the post. It will simply show as a link like this:
http://www.prophotohome.com/forum/ph...medium/175.jpg
Please let me know if you have any other questions.
Thanks,
Drew