One of the biggest problems for making the background look convincing is making sure that the lighting of the background matches the scene. For example, if the sun or lightest part of the sky is to the right of the scene the shadows should go from right to left.  That is a very simplist example I know, but I see so many finished renders where the lighting of the background means it could not have possible lit the scene in the real world.

Using a sky or enviromental dome in Poser can help to avoid this problem.  The other way is either to have in mind which image you are going to use for the background and light the scene accordingly or render as a .PNG and keep going through the images available to find one that matches but that is a long 'hit and miss' process usually. 

I prefer to do backgrounds via post work and then use layers to add the background to the render.  Using this method, there is any depth of field in the render I am able to apply blur to the background layer so it matches.  You can also change the colour balance to match the render in the same way.  Again there are many examples where the render starts to lose focus into the distance and then the background is sharp or the colours simple do not match the scene.  After a while you begin to know what is needed so the time spent in postwork is quite short.

 

 

I use Poser 13 on Windows 11 - For Scene set up I use a Geekcom A5 -  Ryzen 9 5900HX, with 64 gig ram and 3 TB  storage, mini PC with final rendering done on normal sized desktop using an AMD Ryzen Threadipper 1950X CPU, Corsair Hydro H100i CPU cooler, 3XS EVGA GTX 1080i SC with 11g Ram, 4 X 16gig Corsair DDR4 Ram and a Corsair RM 100 PSU .   The desktop is in a remote location with rendering done via Queue Manager which gives me a clearer desktop and quieter computer room.