The easiest way is to use a photo host such as Photobucket. that will even let you do some editing and or resizing before posting it. You can't delete the photo from the host though as it will then disappear fr.om the forum.
You can also post a link to an album on the host and share that way. An example here, this is my album for my 71 GMC, it isn't fancy but it shows what I have been doing to the truck and that isn't much lately.
http://s173.photobucket.com/albums/w...0GMC%20pickup/