Write an article based on this "Open the Layers window. Select the cropped layer. Lower the layer's opacity. Flatten the layers. Export your finished image."
Press either Ctrl+L (Windows) or ⌘ Command+L (Mac) to do so. The Layers window will pop up in the upper-left side of the screen; you should see both the base photo and the cropped layer appear in the photo. Click the layer preview that corresponds to your cropped layer. At the top of the Layers window, click the downward-facing arrow to lower the opacity of the cropped layer. You may have to lower the opacity to 20 (or lower) to achieve your desired effect. Click the Image tab, then click Flatten Image in the resulting drop-down menu. This will combine all of the photos' layers into one image. This step is necessary before you can export the image to an image file. This will allow you to save the image as a JPG or PNG file:  Click File  Click Export...  Enter a file name. Select a save folder. Click Export