I have a model coming over in a couple days to do a shoot. I have chains and restraints and want to do a shoot that an digital artist can put a rock or cave background behind the model as if she is chained to the wall. I will be using a white background, model will be standing with chains coming from above. My question is; Is it better for the artist to have the model against the background or a couple feet in front of the background and back light the background to be pure white. The second question is should I shoot low and upward, straight-on or high shooting down. I thought someone told me a while back to shoot low and upward but not sure. Any helpful on tips or advise would be appreciated.

You honestly could do it any way. If the artist is good, they'll be able to use it.

That being said, there are a few things that you can do which will make their work go faster. Away from the background, and plain white, will make it a lot easier for someone to pluck her out and place her somewhere else but if you want her flush against a wall/rock in the final image, best to do the same with her originally, that way the body contours with the pressure, as it would in the final.

Personally I prefer straight shots as that's how the majority of stock images are. Angles are artistic, mind you, but it may take them longer to find the perfectly matched background, if at all. One can always change perspective, but doing it too much will make the original look funny.

Hope that helps. Feel free to message me if you have any other questions though.

Keep in mind that a white background may cause a reflection on her back that you dont want if she's gonna be having a dark wall behind her. Although it depends on her clothes also.
I would go for a grey background, if you have one.

The angle is easy, google can find you many examples. replacing a white background with a dark one without the model look copy pasted need skill,  you should probably talk with your retoucher.

Chromakey Green Screen best method to replace backgrounds

I've done something like this.
My approach was to photograph the model in a white background.In fact all of my composites have been from a white background.
This would probably be consider 18+ since it's implied.
http://www.digisnapstudio.com/-old-sentiment
https://www.modelmayhem.com/portfolio/pic/37652726

I find it easier to extract the model. You also probably want to think of where the lighting in the final image will come from. And shoot it that way, but also well lit.   If there are going to be heavily shaded areas those can be darken digitally.This will help be more realistic in terms of how the image flows as a staring point in lighting and perspective.
Hope this helps.

Thanks or all the help. I'll spend some time and shoot it different ways and angles. Was a little surprised about you  wanting it well lit. I was going to light it with shadows and more light coming from one side but easy to take some with balanced lighting.  I don't have a retoucher  picked yet. Wanted to make sure I got the shots and look I wanted first. I originally wanted a large chested model as I thought it would give more of the look I was looking for but found a cute smaller chested model with a great figure that wants to work with me so were going to see what we can come up with tomorrow.  Again great ideas and thanks for all the help. I will check the forum tomorrow b-4 the shoot if you guys think of anything else

Another quick question- I was going to use glycerin and water in some of the shots to get a sweaty look. Better to add it in the shot or do it post?

You can have shadows in the manner you expect the final result. Like I said, darker recessed can be darken a lot more digitally. It will be better for quality. So yes, in general you want it well lit.

As far as glycerin and water, it can be done. That can be carried over in the process. Plus will be faster to compose since it will already be there. Just make sure that you check the highlights once you start shooting. You don't want to have over expose areas where the detail cannot be recovered. In most cases I shoot a tat under exposed, to ensure I got the data.

Best of luck!