PTMAN,
Your photograph captures the feeling of motion very well. The composition is balanced well between the still image in the mirror vs. the motion area on the left side of the photo.
One of the comments below mentioned that you should use your graphic editor to rotate the image (I assume they want the mirror perfectly horizontal?). I'm not sure if all side mirrors are mounted parallel to the ground, so will leave this for you to decide. A person viewing this photo could use a stronger horizontal frame of reference, I'm just not sure if that reference should be the mirror. The trees reflecting in the mirror seem to be vertical (no tilt) and this would indicate that a rotation is not necessary. Of course there are no visual cues to indicate the type of terrain either; ie were you driving up or down a steep hill? ;-)
The shutter speed of 1/250 second is effective in capturing the motion here. The upper right corner (black arc) doesn't add anything to the image, and the lower right corner just shows the mirror mount on the vehicle. The composition could possibly be improved by cropping this small amount from the extreme right side.
Really cool patterns in the mirror. I like how you have the stuff in the mirror in focus and the area you are driving past showing the motion. Great angle and framing/cropping. Definately shows motion. Good luck in the challenge.
Now this is something different. Good job of getting in the shade to take this one. Most people are out in the sun when they try this in the rear view mirror. The thing here is you have Focus and non focus presented in a slighty different way.
Not a bad picture.