You gotta use the pen tool to extract the dog from the image and then when you cut the image from the original, make sure you have a 1 or 2 pixel feather to smooth out the edges... Also, the picture should be put more in the background.. what Guitta said about the footprints is very good advice, but what I would suggest is change the ground texture be closer to the dog's texture/colors, that way he doesn't stick out so much... Whatever illumination you use, make sure you give it a orange/yellow filter to match the light color in the dog picture...