Ahh close, you use quotation marks "".
So it looks like this in a spawning event:
Player Spawn bullet on Layer 1 (Image point "gun barrel1")
If you wanted to use image points elsewhere, like setting the bullet towards a point of the ship or something you would use it like this:
Bullet, set angle toward position :
Player.ImagePointX("gun barrel1")
Player.ImagePointY("gun barrel1")