I might implement this kind of thing by having one node for the main, macroscopic scene image, and multiple nodes for the hidden images. The hidden images would be siblings to the main scene image, though they should be rendered on top of it. When one of the hidden images is clicked, their sprite could undergo some effect. You could either modify the sprite directly (by tweening some of its properties using a
Tween node) or create a particle effect for it (using a
Regarding the effect when an object is found, it might be cool to have an expanding and fading particle effect which uses the found object's sprite. You can create the particle when the object is clicked and tween its size and transparency.
You can also change the found object's sprite on screen so that there is a visual indicator that the item was found. For example, if the found object has non-natural color when hidden, you can tween to its natural colors. Or you can create a colored outline around the object that pulsates.
Alternatively, you may want to have some kind of HUD bar on the bottom or right of the scene. When the player clicks on a found object, you can move a copy of the sprite to the bar, maybe with some kind of trailing particle effect.
If the game is targeted at children, you might want to have unique sounds per item found. For example, if a hammer is found, maybe play a hammering sound when the item is clicked. You can easily play sounds using a
Regarding a hint system, maybe have some kind of audio cue when the mouse cursor is near a hidden object. Or have the mouse cursor vibrate.
Just some ideas.
Here is a rough illustration: