camera as viewer
I can't speak for other camera, but on the HX5, I can copy pictures I took from the camera back to the memory card, the HX5 will tell me it's rebuilding its internal database, after a few seconds, it's all viewable again.
That woks well with hx5 photos.
For .jpgs in general, use the export option of the PMB software. Choose the memory card as destiny, and the bigger size preferrably (if you might want to zoom in or output to a TV via cable).