How to do Object Recognition inside a gray-scale image using C#?

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C#

algorithm

Hi,
I am working on a C# project which requires recognition of objects inside an image file. The image will be gray-scale. The objects will be usually some small shapes like circle, rectangle, arrows, semi-circle, and so on. In my problem domain, those objects will be of very small size like only 0.1% to 1% size of the whole image. The difficult part is those objects can be situated on top of some bigger objects. Which means there can be some lines crossing these objects. I must still be able to recognize them without those blocking or touching lines.

So in general I need to select an object using some kind of magic wand like algorithm and add or remove parts from it to refine the object selection. Any help or guide on how to proceed or where to research on or where to get similar algorithms will be helpful. I am totally new to image processing. I worked on many C# projects but this is most challenging to me.