ExcludeRegion can be passed as an optional parameter in the validate Imagium API.

Checkout 1. Rest API - Imagium for more details

Here is how you can generate the rectangles at runtime:

driver.get("https://www.google.com");
WebElement we =   driver.findElement(By.name("q"));
int x = we.getRect().x;
int y = we.getRect().y; 
int w = we.getRect().width; 
int h = we.getRect().height; 
String rectangle = String.valueOf(x)+","+String.valueOf(y)+","+String.valueOf(w)+","+String.valueOf(h);