Detect the centerpoint of an object on grey background

Question

I have many photos I want to center my crop script.
It is done already, but now I want to more:
Is it possible to detect the top right down left sides of the object in the grey background and give me the x,y center of this object?
The object is always surrounded by grey background.
The grey background is almost allways similar and with no dust (almost...).
I can imagine that I could create a rough tile selection (larger or smaller), move it on all the image to read the colour and leave what is similar with the first lefttop reading. Then select al the remains: my object.
But something tells me that there is an easy and smart way of doing this with not much processor saturation.

Answer 1

Doesn't work. I only do this when the backgroung is flat color.
My grey background has smooth variations and it trims the image on all of it, not only the object.
It should be helpful if the trim dialogue could have a fuzziness % to tell what I want to really select.