[Caleb Fulton]

You know the tilt angle of the camera and you know the (x, y) coordinates of the centroid of the blob, so you can make a useful estimate of the distance given the proper transformation which, for simple (FIRST robot) purposes, could be as simple as calling the "distance" to the target the difference between some reference point's y-coordinate and the y-coordinate of the centroid while always keeping the x-coordinate of the centroid at the center of the screen by steering the robot. Of course, this is not an accurate measurement in "feet" (nor is it even linear), but you will get a qualitative estimate that can surely suit your purposes.