the problem is that of a path planning algorithm. the obstacles will be rectangular shaped boxes. what i need to do is detect the rectangular boxes, and then add a black "aura" around these boxes. any ideas on how i go about doing this?

First, you have to detect the object itself. Then you can construct a 3-4-5 triangle, or continue the same length as the base, creating a "T" with one of the sides, and see if lines drawn to the top of the "T" are the same length. There is much info on the web about edge detection and determining shapes. We are coders, not theorists. First you have to decide on a system, then produce the code, then you can ask questions here about your code.