How to select partial part of an image and save the data in 2-D vector

Hi..... please help me if you can , I want to select a a part section of an image using the mouse pointer ( Arrow) [like selecting square part] , only by using the mouse and I wish the answer comes in m function, that the selected data can be stored in a two dimension vector..... thanks in advance for all whom read this or answer.

[Nizar Ahmad]

the Topic of this problem belong to ROI processing in graysclae image