picviewer.skin is ruled by rr.ini variable "picspath"
Either set the "picspath" variable to your picture directory or add a "SETPATH" command after you load picviewer.skin
PICS||SETPATH;<your dir path>
If you want to filter only one file type (i.e. *.jpg only), just create another custom picviewing skin w/ the properties you already provided.
From Skin Commands.txt
/, (SD) Directory List Properties -- (May be Extended later)
/, a Disp w h Path Files ShowExt
/, -- ---- ---- ---- ---- --------- ---------
The above defines extra propperties for the folder List on the current skin.
AA is the Alignment of the Directory List (00=Left, 01=Right, 02=Center).
Disp Mode sets the mode of display (00=Normal List, 01=Thumb Preview Icon List, 02=Thumb Preview Icons).
Note: iLists require that you set Disp Mode to 03
ICOW defines the Width of the Icon to display on display modes 1 and 2.
ICOH defines the Height of the Icon to display on display modes 1 and 2.
PATH defines the Directory/Folder location to display initially (OPTIONAL). If not present the path
from the previous screen is used. Use "DEFAULT" for default path when needed. USE QUOTES.
FILETYPES defines which filetypes to display. i.e. ".jpg,.bmp,.gif" -- "*.*" can be used for all files.
EXTENSION defines if file extensions should be displayed. TRUE for displaying extension, FALSE otherwise.