a simple ''hello world'' image processing app, using OpenCV or equivalent

if you don't like OpenCV, please suggest another library. I would like to learn to write basic image recognition apps. So, let's start from a n00b task as follows. Input file is an image that can contain shapes as follows: - rectangles of any size - letters X, B, P, E, U, O printed in various sizes but using the same font of your choice Shapes will be placed in random positions, including one inside the other (but note that all of these shapes are "connected", for simplicity), but there will be no line intersections. Each shape is drawn only in a single color; background is a single color distinct from that of any of the shapes. There will be no other types of shapes, only these ones. I will make these input pictures using Paint. For each shape in the input the app will print out its type (either "rectangle" or name of letter) and some identifying coordinates, probably UL corner of enclosing rectangle in a listbox (or similar). It should be possible for me to select the shape (e.g. in listbox) and press button "change shape's color to red" which will alter the image appropriately. In short, this should be a 2nd week of intro course type of assignment, involving edge detection, basics of OpenCV and analyzing trivially simple shapes. The app should run on Windows and preferably be in C# or Java. Strongly prefer C#. I really don't want Matlab but will consider if you can only do Matlab and ask a lot less than everybody else. Lowest price wins. I may have further learning simple image processing / ocr type projects in the future, and I definitely don't have money to burn on any single one of them.