Flowers in the hair (or something else!) It's all about layers, the magnetic lasso tool and clipping masks.
This is an adaptation of exercise 17 Masking sunnies.

The original image and the completed image, using two different ideas:

Looks simple enough until you trace through the steps involved.
1/. Find a suitable image to work with. Make sure the focus is on the front, facing the camera.
2/. Find the overlay for the hair. You could use two different images for the overlay of you want (see above).
Image sizes do not matter too much, but recommended 1024px up. They do not need to be the same size. But small images as this will not be as effective.
3/. Ensure in Photoshop the layers are turned on. (Windows/Layers) and this panel will sit on the right side of the window.
4/. File Open the person image first, then the scene.
5/. On the person image Layer/New Layer and name it left side.

6/. Then using the Magnetic Lasso Tool, draw around the hair on the left side.

In using this tool, keep to the borders and do not take your finger off the mouse. When done, double click on the end and this will enable the lasso to be highlighted. The Magnetic Lasso can be moved at each point if you over-run the outline.

Try to be as accurate as possible with lassoing the shape, as it will show later if the shape is out of proportion. Without doubt this is the hardest part of the exercise!

Rough edges look horrible and smooth edges look really great!

Using the Paint Bucket and black paint fill the left side. Then sure you de-select the squiggle around the left lens, by Ctrl D.

7/. Then copy/paste the scene (or what ever you have chosen) onto the person image.
If you need to reposition the top image, use the Move Tool (top of the Toolbar), to position the image to take the best view.

You can adjust the positioning of the image by using the Move Tool.

8/. If you need to align the image better onto the person's left side, use Edit/Transform and the Move Tool (Top of Toolbar) to align your image.
9/. Now with the top layer selected, Layer/Create Clipping Mask. The Background Image, will now fit in the left side. Rename the layer "left side filled".

10/. With the Move Tool, place the section of the left side of the image where you want it to be.

If the overlay is not long enough, fit it to the top, then repeat 6 - 9 above.

Now for the right side:
9/. First, select the original image with the persons right hair. Create a New Layer and ensure it is placed at the top of the layers. Rename the layer right side.
10/. Repeat step 4 above: Using the Magnetic Lasso Tool, draw around the lens of the right side. Using the Paint Bucket and black paint fill the right side.
11/. If you need to align the image better onto the right side, use Edit/Transform and the Move Tool (Top of Toolbar) to align your image.
12/. Now with the top layer selected, Layer/Create Clipping Mask. The Background Image, will now fit in the right side. Rename the layer "right side filled".
13/. With the Move Tool, place the section of the flowers image where you want it to be. Again if the fill is not long enough, repeat steps 6 - 10.

It's your creation - be creative and enjoy!