Mmmm... Well, seeing you're new and are using photoshop, I'll try to help.
In terms of blending any render with any background, smusge that render as so there is a similar colour scheme.
If you don't wish to smudge, lighting, photo filters, C4Ds and gradient maps can help with blending when adding a render to a stock image.
Gradient Maps:Go to Layer>New adjustment layer>Gradient Map. Choose anything. i normally use purple to orange. Set to soft light. Change the opacity to 50% or less, on which gradient map is used and whatever looks good
Photo Filters:Go to Layer>New adjustment layer>Photo Filters. Choose any colour, preferably one similar to your render and BG. Set density to 25 or less.
Lighting:Go Filters>Render>Lightning adjustment (Something like that, can't remember the exact path). Choose Omni setting. Then go Layer>New adjustment layer>Curves. Mess with the curve untill you get something that fits
C4D's: Set to lighten or screen. Erase whatever doesn't look good
Hope this helped.
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