To blend the image with a source photo on an area marked with the Polygonal Lasso:

1. Adjust the Opacity on the left panel (set to 100 to completely replace with the source photo).

2. Click on the image to set the starting point.

3. Move the mouse to draw the first line segment and click to set its end point.

4. Repeat to create additional segments.

5. Double-click to complete the polygon.

To blend with another photo on another part of the image, click on New Selection.