Script to display image1, and after (random ms) show image2 and stop

I've been looking around, and there are a lot of questions (and answers) about changing image after a few seconds, but I didn't find anything that works for me.

What I want;

A script, PHP or Java (prefer PHP to hide function from users) that displays an image1 and after a few milliseconds (500-5000) it changes it to image 2, and stops there.

I have no idea how to create this, so any help would be appreciated..