A really easy and good way to upload pictures is
www.tinypic.com You can choose the size you want it to come out at, and it provides an IMG code for you as well as other styles of links. All you have to do is copy and paste it to your forum message, no need for using the IMG button above the text box.
Another benefit of tinypic is that the link stays good, virtually forever. When you look at older threads there are a lot of broken links from various photo services. Usually due to the service site shifting things around when you add or delete pics from your account, causing the link to no longer be valid. tinypic does not have this issue.
An nothing to sign up to, no account needed, no hassle. It's not a place to host 30 pics from your latest ride or adventure, but for one to a few pics that you want to stay valid, it's great.