Difficulty: Moderately Easy
Step1
Prepare your images. You need an image of a transparent bottle and an image of a ship. Choose carefully, you want the body of the bottle to be big enough to fit the ship (a jug would be perfect.)
Step2
Drag the ship image into the bottle image. The ship image should become the top layer. Make sure the ship image fits comfortably in the bottle or scale it down to fit. If the ship has to be scaled up, find a better image.
Step3
Mask the ship. Select the elements you want to keep and click the "Add Layer Mask" button in the Layers palette. If you need to edit the mask, paint with black to mask and white to reveal directly on the layer mask.
Step4
Duplicate the background (bottle) layer. Move the duplicate layer to the top so that it covers the ship. Mask the bottle in the top layer the same way you masked the ship.
Step5
Change the top layer's blend mode. You can select a new blend mode from the blend mode pulldown menu in the layers palette. "Soft Light" or "Overlay" usually produce the best effects, but you can experiment with other modes.
Step6
Tweak the layer opacity. The value is displayed in the field next to the blend modes menu. You will have to experiment to get the best look, but you want to be able see the ship through the bottle without losing the bottle outline.