Sweep to calculate the average amount of objects that fit within a given area and shape

The matlab code has to be able to look through an entire image and decide the average amount of objects that fall within a "trapezoid stamp" of a specified area given calibration specifications. How would I get started? I got a counter almost working for the whole image, now I just need that counter to work like the description given.

[Matt Kindig]

Can you post an illustration of what you are trying to do? How is the trapezoid stamp defined?

[Image Analyst]

Is this homework? Did your instructor give you any theory to get started? Can the trapezoids be at any arbitrary angle? If you put a bunch of puzzle pieces on the table and corral them with a string then mask that with a trapezoid, you'll have a count of objects that completely fit inside the trapezoid. If you do it again, with the pieces in different orientations, you'll get a different count. Is that what you want to do?

[Angel]

There is a specific trapezoid that is wanted but for a general help, this does not matter as much. Yes, this is what I want. Any help is appreciated.

[Matt Kindig]

Again, could you post an image illustrating what you are trying to do? It is still not really clear what your goal is.