How to detect letters in an image? I have a project that requires detecting and processing letters in a given input image. I am also new to subject of image processing. There are lots of subsubjects in image processing. I believe I don't have to learn all the concepts of image processing to achive my purpose.

Question above; how can I detect letters in a given input image?
Note: I already know matlab. I need to do this by implementing algorithm, not by a built-in function.

I am gonna tell my thoughts. I want to write an application which takes an input image as an argument. If there is are English letters on that image (photo), it will detect them by circling each of the letters. I don't know which subject in digital image processing I must look at.
The field is knows as Optical Character Recognition (OCR) and it's a broad field.

Since it's clearly an academic exercise, you can keep it simple. Start by image segmentation : find shapes where a shape is just a set of connected pixels. [1] Then compare the shapes to known shapes. Don't expect an exact match, do an approximate match. What overall properties can you reliably determine for the shape? Aspect ratio? Holes in the middle?

[1] At this point, you can already draw circles around each shape that's not too big nor too small.