I understand the process of airflow and i've put some holes for ventilation in the frame. I thought about fans but i dont know how to power them, seeing as how the laptop motherboard in there doesn't have any power connectors. I did leave the stock cpu heatsink/fan combo on the cpu, but it cant seem to handle the cooling alone for the 16"x20" frame.
At this point I think the only options you have is to find a power source some where on the motherboard or bring in your own with an adapter from radio shack. You may be able to solder wires onto the power jack for the AC adapter if you feel you have the skills to solder in that small of an area. That would probably give you 12v DC to work with (Although most smaller fans IIRC are 5v).
OP doesn't have room fro 120mm fans. Likely will have to use 25 or 30mm and in order to reliably move the air a pair of them will likely be required considering the volume of box we are working with. Most laptops have an in and an out on them for this very reason.
then again, a self-contained picture frame is a lot smaller then a cabinet. a single 60mm fan will probably do the job. I've never seen a laptop under $1000 that isn't Pentium 4M that has more then one fan.
Maybe... but I doubt it. My guess is that the shadow box isn't that thick so there a) isn't room for a 60mm and b) there isn't much space to channel air, hence the fans need to help it along.
Your point about the fans, while I doubt that it is as common as you think to not have two fans of some kind, is irrelevant to this scenario. Why? Laptops suck in air and exhaust it right back out (in the case of the CPU fan). That hot air doesn't stay inside the case. Inside the shadow box he is sucking air in that is inside the box, blowing it over the CPU, and then pushing it right back INTO the box again. Look at any laptop, I'd put money on the CPU fan being semi-circular pulling in from the back and pushing out the side (or vice-versa). The problem is the air never leaves the box.