Are you needing to send a PM with a photo attached within it? If so I think it's the same process as posting a picture within a regular posting on the forum. i.e. it needs to be already online someplace like Photobucket and you create a link to it within the PM you're trying to send.
That's the way I've always done it. Hope this helps. Sorry if I'm talking out the back of my head, I stand ready to be corrected if people have a better solution.
Here's a walk through for you. Assuming you want to send a picture that is ALREADY online someplace, such as at a public website. This works best if you open these as new windows or tabs within your browser.
1, Go to google and chose the images option at the top of the page before Maps. Then I typed cats in the search bar. (this is just an example for ease in this little tutorial)
2, Have a browse through the image results shown and find the image that suits what you want. Click on that image.
When the new page or tab has opened it looks something like this:
click on the link so you know what I'm referring to.
3, Now right click on the image of the cat in the main screen and select "copy image location"
How ya doing so far? Good I hope.
4, Now if you're typing a PM, or making a posting here, and you want to include the image of the cat you can say for example
I found this cute image of a cat today here itis
What I did was after the underlined word "IS" above I wrote [img] then I right clicked and selected paste and the link I previously copied appeared, then I wrote [/img]
By doing this you are making an image link for the forum to connect to the image that exists already online and makes that image appear in your PM or posting. It sounds clever and oh so impressive but it's only something I picked up just recently and it's dead easy to do. Just remember to press the [ key and not the high case version of it which is { same with the closing bracket ] not }
Simples!
If you're wanting to show an image that you took as a photo for example, you need to upload those images online to a host website such as flickr or photobucket then link to them in the similar way I described above. Please don't go thinking I'm clever at this sort of thing, it's just something I picked up and use a lot.