Make a new canvas, we used 600*480 px here, but the size is of course optional.
Select the Gradient Tool, using two shades of blue (see below), fill your canvas, so that the darker colour will be on top.
Take a photo of a girl. If needed, resize her so that she will fit in.
Make a new Layer. Make sure your primarily and secondary colours are black and white. Go to Filter >> Render >> Clouds
And, if needed apply the clouds effect a several times to achieve the desired randomly “clouded” effect.