Color of a pixel independently of the browser and resolution

I want to build a tool which can give back to the user the color of pixels of a image, for this I found how to do, with java.awt.Robot it's quite easy

But the problem is (it just came to me after one week coding ^^) that because it's from a web page, the position of each pixel i want to get back the values (there is about 5 pixel i want) will be dependant of the resolution of the screen and the browser (the image won't be exactly at the same height on Chrome than on Mozilla), if you have download someting recently you'll have a bar at the bottom ...

But apparently the picture has always a size of 330*422 so many I have to calculate the absolute position of a corner a the image from the corner of th screen and then apply relative positions from this corner to find the pixel I want ? I know a bit of JsoupParser and Dom but becase of how the page is made not sure i'll help

So not sure there is an issue, but I'm here to ask help to find a solution if there is one ;)

(In case you want to see : http://ift.tt/2l2xUrl, there is some items of the guy which can change and i want to look at it like every 5-10 minutes by )