Should I Use A Sample Pic?
Well the upside to this is you'll get more hits... depending on the quality of you're pic, the speed of you're server etc... A lot of people are going to look at this pic and use it to gauge you're entire site before visiting it.  If its a bad pic, it most likely won't get you hits but could work against you.
Also there is an issue of bandwidth, you're going to have to pay for the transfer of this pic every time it gets hit.  So be careful.  If you can't afford it, don't ask for it. If you think you might have to back out of this, please be sure to email me letting me know you don't want the sample pic listed any more.
Finally if you're on a free host, do NOT submit a sample pic as all free hosts will seriously have a fit if I try to link to a pic on their server.