I won't be claiming you are scamming or the like, but this is a big downside to your project
After your purchase I send you a link to a zip file containing your image. It will destroy itself once opened once. Be sure to save the image. Also I will send you a Bitcoin address belonging to the image. All Bitcoins you send to it are then on the offline wallet stored inside the image. To retrieve Bitcoins from the image you at the moment have to contact me (send me the image, how many Bitcoins to retrieve and the receiver Bitcoin address).
So we do need to contact you to withdraw from that wallet? That would take out the meaning in having your own wallet anyway, And if you no longer provide this service then these coins would be stuck?