I've added the "Simple Image Upload" to the forum. This allows you to add images to your posts by clicking on the "Add image to post" link at the bottom of the Message Body window.
This stores the images on an external web server (postimage.org)
There is a size limit for images. If you have a program like Adobe Photoshop, I suggest the following process:
Open youd image in Photoshop (left click on file - open - and select your file from where ever you savex it)
Select Image - resize - image size
Set the longest axis at 800-1000 pixels.
Save the image using the 'save as' function and give it a different name (I just add 'sml' to the original file name so that I know which image I have reduced).
When it asks for 'JPEG options' set the 'image quality' at '5' (medium) or '3 (low).
This will give you a reasonable quality image at a reasonable size.