How can you change human pose into mannequin like in these images? And what tools will be required to do that and how?
Not everything is done in Photoshop.
A dedicated 3D application is used on those images.
Choose an application. In this example Blender.
Learn how to sculpt what you need. In this case, I am downloading an already made hair and head.
- Adjust light and material. Render.
Now, on Ps
- Remove the unwanted background.
- Mask and compose.
I made a very lazy work. Making it right takes time. You need to understand how the 3D software works, some light and photography principles besides using masking and layers on Ps to compose it.
If the conditions of the face are suitable, you can play with it to make it look plastic or matt metalic. Things to consider when creating realistic highlights and dark reflections on metallic surfaces
You can colorize plain head, body and limb areas, fade their features and take parts from other photos to replace them.
Taking parts from other photos leads easily plausibility problems because sizes, placements, positions viewing directions, lights and shadows must all fit. It's not beginner's job.
One possible source for replacement parts is a 3D human body and posing application. Another possibility is to shoot photos of a real mannequin or adjustable enough lay figure. Unfortunately I do not have such things.
Recolorization and fading features are easier. This is my example (an image copied from a local news site):
Start by making careful selections of the live areas. Forget the magic wand. Polygonal lasso and drawing paths are accurate enough. Sometimes also the quick selection tool can be used. The needed skill set is the same as in detailed background removal jobs. Cut and paste the live areas to a new layer:
Clone a little of the evironment inside the empty space left by the moved live areas. You need it because otherwise there would occur an easy to see border. You need the expanded background also to have some room to change the forms of the live areas. I cloned more than I need:
Content aware delete instead of cloning can be useful.
Make a couple of copies of the live area layer to be sure you have also a spare in case of errors. Remove the color from one by applying Image > Adjustments > Desaturate. Reduce the contrast with curves. There's no full black nor full white point:
Make it look artificial by applying Plastic Wrap filter:
Insert single hue color by applying Image > Adjustments > Hue&Saturation > Colorize
Clean edges by deleting a narrow manual selections, fade some too fine features by applying healing brush and clone stamp tools. Remember: To cut something at the edges need a cloned backround below. It's done in my case:
Plastic Wrap like many other filters make not so well defined result near the edges. A good way to get solid edges is make a selection and drag stuff against the selection border with the smudge tool or cloning stamp. They are both used here.
If you need more artificial head you must either paint it or copy it from elsewhere. No filter is clever enough to draw automatically the ellipsoid which fits into the pose and light conditions.
BTW. If you have a good pose and fine clothes photographed with a live model the reason to change a statue inside the same clothes is not so clear. You may think you save some money because you don't use the model. But that doesn't undo the fact that model stood inside the clothes and his image is used, no matter how heavily it's processed. Check what's written in the contract and ask a lawyer what you can do legally.