Are you using photobucket?
if you are its super easy...
1. log in to your photobucket account.
2. click on your album that the desired picture is in.
3. click on said picture.
4. off to the right there will be a bos that says "share this picture, and under it will be a box of "codes"
5. click and copy the code that says IMG Code, its the very last code.
6. come back here, and paste the code in the reply box, it should look like this to you in the reply box.
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Just without the double hyphens after and before the
now, when you click post reply it should post the picture like so