greasemonkey -blocking dynamic image

[mash0]

Hello everyone i'm using this code and its not mine on greasemonkey to replace an image with another

my problem is that the website i'm visting  have dynamic content and the whole images keep reloading without i do refresh /f5 for page

 

 

now how i can make the script call the the image "i want to see"   every minute

var images = document.getElementsByTagName ("img");
var x=0;
while(x<images.length)
{
if(images[x].alt == "image i dont want to see")
{
images[x].src = "image i want to see";
}
x=x+1;

}

thanksss