It seems quite easy.
Use the gradient fill tool with a light purple and dark purple to create the coloured background. Take your subject picture and lay it on top of the coloured background.
Right-click the layer and select Blending Options. Drag the 'This Layer' right-slider to the left to reveal the background layer. Keep sliding it until you're happy with the result - you can also hold down Alt and split the slider in two to improve the blending.
Click Image > Adjustments > Black & White. In here, you can adjust the contrast on different colours, to increase or decrease the detail in your final image.
The pinkish Les Amours Imaginaires picture appears to have some kind of water colour filter applied to it. The pic below has a grain filter applied.
Dry brush filter;