The only addendum I'd make there is that sometimes .rsr or .png files can be the thumbnails for the other Poser file formats;

e.g. if you have a "figure.cr2" file you might have a "figure.png" thumbnail sitting alongside it.

I've found a few freebies... and even older marketplace products that still have .rsr files for the thumbnails... and had to convert these to .png format, so that the thumbnails would show up in my Poser Library, on my mac.