Masking an undefined shape using the "color range" selection tool.Add the fire to a new layer above the cabin background.Open "select/color range" to load the color range selection tool. Set the fuzziness to approximately 180, leaving all other settings at default. Click on on the darker area of the fire, then hold the "shift" key and click on the bright center to add it to the selection.With the selection now active, add a layer mask to the campfire layer (the layer mask button is at the bottom of the layer pallet and looks like a rectangle with a circle inside it). Your image should now look something like this: