To attach a photo in your signature you need to have a online photo host.
After you upload you picture then put the url in the IMG spot when editing your signature.
You can use the same way to attach a photo to a text message if it is not available in that forum.
There are only a few forums where you can insert a pic. Then you just choose the browse at the bottom of the reply and upload it directly from your pc.
Hope that answers you question!
