This is probably going to depend on the policy of the particular forum
you are posting to. I would check to see if they have an FAQ that
permits posting. You may want to post the how-to question on that
forum.
At any rate, here are some things to try:
Option 1:
Upload the picture to Picasa Web Albums. Each picture on the detail
page has a link that says "Embed in Blog/ Myspace". Click that link can
copy the little bit of code that appears and paste that into your forum
post. This may or may not work.
Option 2.
Some forums have special syntax to use to post to forms. Try right
clicking the picture in the picasa web album you want to embed , choose
"Copy picture location" then go to your forums post and pat that link
between the following [img] Paste here [/img] again, this may or may
not work.
Option 3.
Upload the pictures to a picasa web album. Then copy the URL of that
album. then write in your forum post: See my hunting pictures here:
http://picasaweb.google.com/yourname/youralbum
Some forum software will automatically turn that into a link for you.
Sorry, I can't be more specific. Each forum is a little different.
Mike