Can hair be taken from elsewhere than the hair on your head, or can you use someone else hair?

Theoretically hair can be transplanted from any part of the body to another. The only issue is that the hair will retain it's initial texture, length, color, etc. so it may not look appropriate depending on where the hair is being transplanted from. This is why we prefer to take hair from the scalp for hair restoration before considering anywhere else.
You can't transplant hair from one person to another, however.

Hair
cannot be transplanted with success from one person to the next.   Transplanting your scalp hair to other areas
on your scalp usually gives the most natural appearance in terms of texture,
color and growth cycle.   However, when
the donor area becomes depleted, the beard, chest, back, and extremity hair may
be used.