I have this gallery which I want to add a floating effect to. I tried this code but it is not really what I am looking for. I want to add an effect like the one on this gallery.

This is my current code:

Actionscript Code:
const SPEED_MULTIPLIER:Number = 5

var speedX:Number = 0
var speedY:Number = 0
var upperLeftLimit:Point = new Point(0, 0)
var bottomRightLimit:Point = new Point(500, 500)

addEventListener(Event.ENTER_FRAME, routine)

function routine(e:Event) {
    speedX += Math.random() * SPEED_MULTIPLIER - SPEED_MULTIPLIER / 2
    speedY += Math.random() * SPEED_MULTIPLIER - SPEED_MULTIPLIER / 2

    if (thumbnail_group.x + speedX > upperLeftLimit.x && thumbnail_group.x + speedX < bottomRightLimit.x)
        thumbnail_group.x += speedX
    else
        speedX = 0
        
    if (thumbnail_group.y + speedY > upperLeftLimit.y && thumbnail_group.y + speedY < bottomRightLimit.y)
        thumbnail_group.y += speedY
    else
        speedY = 0
}

Please help