Open several images shot from tripod
1. select the move tool and Shift/drag image 2 and 3 onto image 1
Holding the shift while dragging the images will place them in exact register.
2. change the layer blending mode of layer 2 and 3 to lighten (or screen)
Experiment with other choices for other effects.
3. add layer mask to layer 2 and 3. Mask any areas where the layer stacking
adds noticeable brightening in unwanted areas.
4. add a levels adjustment layer to each layer to fine tune
brightness and contrast individually.