Chrome App Grid Image

i need a Chrome App for verify in any image of my browser the proportion of text that contain. But you dont need read this image anyway, you can make this way: example: You can divide image in 25 equal squares, before click, in some "grid style" with equal proportion, lines and columns equal and after that i can click in this blocks and in somewhere you want shows me how many blocks in percentage represent of total. i.e: 5 blocks 20% (total proportion of image) I don't understand of chrome app permissions, but needs permission for see images and i want collect some e-mails of people who use this app. No more features, just useful tool for my work.