document.getElementById("picture").src = "/img/cool-picture.jpg";

Now comes the glitch in (guess where) Internet Explorer: If you want to reload a picture that has changed on the server (let’s say you have overwritten the picture with a php gd-lib script in the background), the Internet Explorer (i call him msie, spoken “emsy”) always keeps the cached picture instead of reloading the picture from the server like opera and firefox do.
You can fix this behaviour with a simple cache-avoiding technique: Add a random number as a parameter, as shown in the following code, that’s it.

document.getElementById("picture").src = "/img/cool-picture.jpg?r=" + Math.floor(Math.random() * 1000);