1. Click the "+" icon in the source window to overlay the current source to the PGM

   

2. If the source is 32-bit and contains alpha channels, it will be transparently overlayed.

     

3. Open the attribute window of the source, click "Layer", select "Main" layer, and use "pan", "zoom", "rotate" and other operations to adjust the image.

     

4. Overlaying multiple sources, you can mosaic multiple images at will.