print message,different pixels in image

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hello there!

i am able to find out the difference between pixels in each frame(so i can find out if there are differences in each frame ) if there is a difference i am printing a message i there is not i am printing an another

my question is coming now: i want to group those messages , like the following example lets say that i have a video that in the first 20 frames something is changing and after those 20 frames , there is immobility for 10 more frames (no difference between pixels ) , and again activity in my video for another 30 frames

so i want a meesage like this! "the object moved 1 time" "the object stayed stable " "the object moved again"

ANY IDEA HOW TO DO IT??? thank u in advance!