Resizing Pixel Images

How does the user re-size a picture when they 'buy pixels'? I can move the picture around on the grid, but can't see how to re-size. This would be very useful so that the user (buyer) can make the picture the actual size they want to purchase, rather than having to ensure proper sizing befcre uploading. Would be very useful for someone that wanted to get a smaller image because of cost. If user has to go external and re-create image for exact size, they will probably just give up on the whole thing...and that's a lost sale.