Find or take a picture of your subject facing the camera.
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Open the image in Photoshop.
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Make sure the Contextual Task Bar (the gray bar under the picture) is on. If it isn’t you can turn it on here:
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On the task bar, choose “select subject.”
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Your subject will be surrounded by the marching ants.
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On the left side of the screen, select the polygonal lasso tool.
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Set the tool to “subtract from selection.”
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draw a shape around the side you want to stay unchanged. You’ll have to be careful on the side in the middle of the face, but you can made a large selection on the other side. Your line will be gray as you do this, but it’s shown here in red to make it easier to see.
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When you close your selection, the marching ants will only be around one side of the subject.
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Press command-J to jump the selection to a new layer. Your layer panel will look like this:
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Make sure you are on the layer with half of the subject. From the top menu, select Filter/Liquify.
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Your half subect will be loaded into the liquify filter.
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Select the freeze mask tool.
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Draw a thin line along the edge of the image. It doesn’t need to be perfectly straight.
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Use the other liquify tools to distort your monster side.
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When you finish warping the layer, select the OK button to accept your changes.
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Your monster layer will now be on top. You might see some of the original picture below it, but that’s fine.
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Go to Hue/Saturation.
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Adjust the hue, saturation, and lightness however you like.
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Find an image to use as your background. I’m using this.
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Place your background on a layer between the original image and the monster face.
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Use the transform tool to fit the image behind the monster. Don’t worry if you see part of it sticking out.
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Use the mask tool to hide the part of the background that’s sticking out.
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Finished project:
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Photopea version: