How to detect checked box in scanned form (PDF) using R?

My question is: Can I use optical mark recognition (OMR) in R to detect a checked box in a scanned standardized form like the one below?

I am familiar with OCR - e.g. tesseract - which has proven useless for the detection of a checked box as there is no distinguishable pattern between extracted characters (Varied from no characters being extracted to "[:]" to "EI" to "E1" to "%" and so on).