My second try with some additional edits and enhancements!

 

 

My finished product. I took the advise of adding shadows. I found this a little more difficult then I first imagined. I also added some warping effects to the text. Below you will find my sketch and copies of the photo original photo and images which I used.  I hope I did the Alien and his friends justice! As for the cow what can I say, he is about to be lunch.