There are 2 ways to do this
The first and easiest is to use PhotoBucket
So if you don't already have your pics stored there, go set yourself up an account
Okay so you hit reply and it opens up a new message
type in your subject
You choose the pic..tag you want to use in photobucket and click on the image code..it copies it.
then up top where you see 3 rows of things....go to secong row...click on the second square
a little window opens up..click in the black area and click paste then the ok button.
then at the bottom of reply window click on send.
You can also preview your post before sending if you want

Second way to post a pic, tag is:
Click on reply
type in your subject
click on first block in second row, window will pop up click browse..it should take you to your pics on your pc
open pic you want to use...click Host it
click on second one: Image: click copy
Go back to top..click one second block in second row...click in black area..click paste then Ok
Click send.