I need to fire an event on a div when div come to a screen window

hi

I need to fire an event from a div
when div come to a screen window of user mean as when he scroll down the page then which ever the div comes it should fire an event

for example

say i have a page in that page i ahve 50 div and each div have 50 images

so now say on page load 1st image is load, now when i scroll down and as soon as second dive come to screen second image get loaded

so i need to know how i came to know that particular dive come in screen

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