How to determine a region of interest and then crop an image using OpenCV

Question

I asked a similar question here but that is focused more on tesseract.

I have a sample image as below. I would like to make the white square my Region of Interest a

Answer 1

Seeing that the text is the only large blob, and everything else is barely larger than a pixel, a simple morphological opening should suffice

You can do this in opencv or with imagemagic

Afterwards the white rectangle should be the only thing left in the image. You can find it with opencvs findcontours, with the CvBlobs library for opencv or with the imagemagick -crop function

Here is your image with 2 steps of erosion followed by 2 steps of dilation applied: You can simply plug this image into the opencv findContours function as in the Squares tutorial example to get the position