i´m not sure if A4 supports tga format. test it.
open up both pics in photoshop, select the b&w one with ctrl/a. copy it with ctrl/c to the clipboard. select the coloured pic, open the layers menu, change to channels and add a new alpha channel. now select this channel and press ctrl/v to insert the b&w one into the channel. save this pic as 32bit tga. here we go.