the best way to do it 'in my opinion' is to open an account with www.photobucket.com
once you upload a picture to them and view it in your gallery, there will be an "IMG" tag right underneath it. Simply copy and paste the tag into your post.
I have to disagree slightly. If you at work like I am and are behind a firewall it doesn't always let you access photobucket. Also it blocks all pictures that are in peoples posts that are done on photobucket so all I see is xxxxx. I of course can see them at home. I know that I can't use photobucket here so what I do is save the pictures on my computer then use Microsoft Photo Editor. I have discovered that it will allow you to edit the size and anything else that you want. Always have to find ways to get around Big Brother. But if I am at home photobucket is the best, imo.