I want to detect collision between two objects based on the image. I can use hittest for this, but I want the collision to be true when object A hits object B's image instead of object B's bounding box.

Example: Say I have an arch. If object A goes inside the arch (not touching it), it will register as a hit, although I never acutally touched the image. How can I say that the hit is true only when object A touches the image?
Thanks to all of you who answered so far. I'll have to try these when I get home tonight. Thanks! Still looking for answers though.

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