It's best to host the pictures on the internet instead of trying to upload them here. I like to use
http://www.photobucket.com as it is very easy to learn and use and on top of that, it's free. You can upload most any size pictures and they are automatically resized on photobucket.
Once you get the pictures on photobucket, you will see these 4 options below each picture-
Email & IM
Direct Link
HTML Code
IMG Code
All you have to do is put your cursor over the 4th choice, IMG Code, click copy then paste it in the reply box when making a post. When you hit submit your post, your picture is there.
When I post pictures, I have 2 windows open, 1 with Photobucket and the other is the message board I'm posting on. Doing so makes it real easy to work between the 2 websites.
I hope all that made sense.
