Compare pixels

[Sablerock]

Guys
I need to compare 2 png images A and B. Identical number of pixels. If pixel(x,y) from A is lighter(whiter) than B, then move A to B.
I did search the board, nothing came up.
Is there a script for this?
Many thanks

[Kukurykus]

Upload examplary files to compare.

[Stephen_A_Marsh]

Layer the file that may have lighter pixels over the other file (2 layers). In the upper layer file, set the blend mode to lighten. Merge or flatten the layers.