Adjust your settings. It's the spill on her face that is causing the problem. Keying is not a one click problem.
Thank you Rick for your reply. I have been playing around with the settings and so far have had no luck. It appears to mainly happen when her face is in front of the black shirt. On all the shots I am having problems, this has been the case.
This could be a tough one; as Rick says, chroma keying isn't a single click and you're done.
Since you new to it, you should know that your chroma key background is REALLY hot, which is causing problems. Ideally, it should be a couple of stops darker than the bright part of the subject. If you're looking on a waveform monitor, the bright parts would be at 100 IRE and the chroma key background at 70-75.
The type of camera also makes a difference: a DSLR stinks for chroma key work, for instance. The codec in which it records throws away about 3/4 of the color detail in the image. Enough remains to fool the human eye, but not a computer. Since a good chroma key is all about the edges between subject and background, having good color detail for a color key is pretty important.
How far away was the subject from the screen?
Which key plug-in are you using? (Hopefully Keylight.)
I would suggest watching this video. Skip to around the 9 minute mark, to see the software side of keying.
Part of the talent's face is slightly caved in after I apply a background. When I remove the background, it looks normal,
Actually, it doesn't look normal in the original footage either. Look closer. It appears that her face is cut off there too - though not as immediately obvious.
Is this footage directly from a camera? What camera? It appears to be either something about how the camera's image processor deals with images or how the compression scheme the camera uses deals with it. It may have to do with the luminance values at edges. There is very little luminance difference between her face and the green screen, but there is between her face and her shirt. Her face looks very soft against the green, but very sharp against the shirt.
Actually, looking closely at the edge of her face and her shirt, notice how there's an odd darker line there? That often comes from oversharpening. Does your camera have any sharpness settings you can adjust? If so, you want to turn it off completely, or put it to the lowest number you can because that might be part of it. If you need it to be sharpened, you can apply a sharpening effect in AE after you pull the color key. In-camera sharpening is killer for post work - especially chroma keying.
Dave's advice about your background being too hot is also correct. If it were a bit darker, this problem might be minimized.
I realized after I uploaded it, I hadn't removed all of the effects I applied. I will try again. And I'm using an old Panasonic DVX 100b (haven't moved up to HD yet).
Yes, I'm using Keylight. Thank you, I'm going to check out the video right now.