I've upgraded the forum software, and the way to include pictures and documents in messages has changed.
To attach a photo or document to your message, when composing the message, click on the paperclip icon 
in the row of formatting icons. Then click on "Upload new file(s)", and either drag and drop your picture/document or use "Add file(s)". Finally, click "Start Uploads".
Photos will be resized if necessary.
The maximum file size is 2Mb - if that's a problem, pleased let me know.