Original image

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Select Edit>Copy.
Select the New Document.
Select Edit>Paste.

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Mask the cow's forward leg including shoulder muscle.
Exit Quick Mask Mode.
CTRL/SHIFT/I to invert selection.
Select Edit>Cut.
Create New Layer. Select Edit>Paste.

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Select the clone stamp to fill in the hole left by the cow leg.

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Return to cow image. Drag and drop the cow's body into new image. Drag and drop the cow's legs into the new image.
Exit all images except the new image.

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Hide the background layer.
Merge visible.

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Select a purple color.
Select Gradient tool. Draw a vertical line down the middle of the image.

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Select Edit>Transform>Scale to make the Cow a little smaller.
Open image of the moon. Select the moon. Copy and paste it to the cow image. Place it at the bottom so that only the top 3/4 is showing.
Select a star shaped brush at about 29 pixels. Pain them onto the background layer, and the cow layer streaming from the cow's udders.

- : source
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Use overlay to blend the moon in with the background. make sure that the moon layer is above the blue photo filter layer.

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Use a small, soft, round brush to make shooting stars. If you're using a pen, select the airbrush tool.

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Select Bevel and Emboss.

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Final result

