Algorithm to Detect flaw and burr on print characters

Hi,
I am thinking about an algorithm for checking flaw and burr on print characters but still gets stuck.
The attached image illustrating of flaw on characters.

Could you suggest some algorithms for detecting flaw and burr on print characters?
I tried image subtraction but that doesn't work because of some problems.

1. This method requires two images are extremely exact in position.
2. Some print characters (without burr and flaw) are thinner or thicker than
the reference image.

For these reasons, that method can't apply.

A Quick Bump!

Can someone help?

Thank you very much!!