is Javascript able to unload an image from an HTML page?

The comments on your question are correct, you can remove it from the DOM, but the browser will clear it from memory when it decides it's good and ready.

To clear it from the DOM, you would do something like this:

var badImage = document.querySelector("img#idOfImage"); 
//or "img[href='nameofimagefile.jpeg']" 
//whatever you need to do to get the right element
//then, remove it:

badImage.parentElement.removeChild(badImage);

$('#myDiv').remove();

or

function removeElement(divNum) {
    var d = document.getElementById('myDiv');
    var olddiv = document.getElementById(divNum);
    d.removeChild(olddiv);
}

Would remove it from the DOM however it won't free up any memory, or bandwidth or http requests...so performance wise it won't make much of a difference (not taking rendering into account).

However I believe if the image is removed from the DOM the memory it uses will eventually be managed and removed by the browser (garbage collection).

So in short no I don't think there is a specific way to remove it from memory because that is a browser-level concern..