Detect rectangular objects on artificial image

hello,

I have this artifficial image which has square objects. i have to do the following: (photo at the end)

1step :

• seperate all "rectangular" objects to analyse them separately

2step

• analyze each one and identify if its a "card" , a "domino"(rectangular shape) or just one greek number (square), or squared noise

There is a small condition met by the artificial image that i beleieve that is very helpfull:

• all the object will be delimited by a black line box and imideatly inside there will be a white line box. see image bellow

Help would be aprecciated mainly to the first step.

Thanks.