You can include screenshots in your reply either by using attachments or links to an image sharing site where you have uploaded your files.
Attachments
1. Click the Manage Attachments button below your reply message box
2. Click the Browse button at the top left to select the file
3. Click the Upload button at the top right
4. Click the Close This Windows button at the bottom to return to the reply window
5. Click the Submit Reply button to complete
Image sharing sites:
http://imageshack.us
http://photobucket.com