I had the same problem like you.
Now listen carefully, here's what you do:
If your image is called cateye.gif (for example) you first have to upload it on a web-page. I used http://www.imageshack.us
. upload it there, then you have to edit your post.
( to do so, you make a post, then click on edit on your post)
When you are there, FIRST click on 'Create a link to a webpage' and write the URL when you will be asked to.
(They will ask twice, so write the same twice!)
SECOND when youve done this you have to click 'Enter an image', write the same URL as before (by 'Create a link to a webpage')
Then you just click: 'Change post' and youre image is there!