Attached Link: http://www.senosoft.com/

You mean an RSR thumbnail for a Poser 4 library item? Reduce your render to 91x91 pixels, and convert to PNG format; at which point it will be suitable for all versions of Poser from ProPack onwards. To make it compatible with Poser 4, use the PNG to RSR conversion facility in P3dO Explorer. (Free download at the link if you don't already have it.) (edited to remove stuttering)