Today’s Question: Is there a way to combine two (or more) photos into a composite image in Lightroom Classic?
Tim’s Quick Answer: To combine two or more images into a composite image you would need to send the images to Photoshop from Lightroom Classic. The only options for merging multiple images together directly in Lightroom Classic are to create a high dynamic range (HDR) image, a composite panorama, or an HDR panorama.
More Detail: Lightroom Classic can blend multiple exposures into an HDR or multiple frames into a composite image. It can even perform both tasks in one process to create an HDR panorama. However, it isn’t able to combine images into a composite, such as if you were replacing the sky in one image using the sky from another image. That type of composite image would require Photoshop.
To get started in Lightroom Classic you can select the two (or more) images you want to combine into a composite image. Then go to the menu and choose Photo > Edit In > Open as Layers in Photoshop. This will open the selected images into a single layered document in Photoshop.
At that point you can use layer masks to combine various image elements, blend modes to combine the images such as for a multiple exposure effect, or otherwise work with the layers to create a composite image. When you’re finished simply choose File > Save to save the resulting image with layers intact (based on the External Editing settings in Preferences in Lightroom Classic) and close the image.
When you go back to Lightroom Classic the composite image can be found in the same folder as the source images used to create the composite.

