Is there anyway to register a click on an image, ignoring transparent pixels, in JavaScript? (like if they clicked on a circle, or a blob)

So I understand how to calculate if the user clicked inside a rectangle, but is there anyway to register a click on the canvas that is on top of a blob, but not inside the rectangle that defines the blob image? Like the image is a blob with the rest of it being transparent pixels, but I don't know how to (or if) JavaScript can recognize if they clicked inside it.