To get the background color of an image

[jomla]

Hi at all

I'ld like to know if it is possible to get the background color that there is in a particular position of an image.
Infact If I have an image and I want to write on the image I want to use a different color then the background to see best my write.
IE:
Image where I write on is black therefore I want to write with white color.

Thanks