thats pretty easy to do actually, just take a pic of it hood up hood down, crop the engine out, fluff the edges a little bit, crop the hood and turn the opacity down a little.
here's one way i can think of.... take a picture with the hood closed, and take a picture with the hood off. open the pic with the hood off in photoshop, paste the pic with the hood closed over top the original as a second layer, outline the hood and define transparency...