The visible part-line of hair in the picture can look a bit absurd. But you can easily darken the hair part line using Photoshop so that the picture looks better and normal.
Step 1: After you have opened your image in Photoshop, create a duplicate layer of the background layer by Layer>Duplicate Layer or by pressing ctrl+J. To confirm the duplication go to Window>Layer or press F7, and name the new layer as Layer 1.
Step 2: Chane the blending mode of Layer 1 to Multiply, this will darken the image.
And you are half done to darken hair part line using Photoshop.
Step 3: But now the whole image is darkened, and that is something we definitely don’t want. So do this Layer>Layer Mask> Hide All. This will bring the image back to normal. But now in the layer panel, you will see a black rectangular box adjacent to layer 1 thumbnail. This black box is your layer mask.
Step 4: Next in the process of darkening hair part line using Photoshop you grab the Brush tool- either by pressing Shift+B repeatedly until it shows up or by grabbing the Brush tool from Tool Panel.
Set the brush size accordingly, but keep in mind to reduce the hardness to 0%, and set the foreground color to white. Now paint the area of the highlighted part-line, this will do the work of darkening it.
Step 5: If you think it has darkened too much, you can reduce the opacity of layer 1 according to your wish.
And thus, you have a darkened hair part line using Photoshop.