MassConv converts whole directories of image files.
Edit by : The program is console and GUI based.MassConv converts whole directories of images in different formats, including JPEG, PNG, BMP, TIFF etc. It generates a new identical to the old directory structure where it puts the newly converted files. MassConv also supports filters.
SUPPORTED FORMATS:

Input:

GIF
PGM
PPM
PNG
TGA
TIFF
JPEG
PCX
Photoshop PSD
Windows BMP
Amiga IFF
SGI
Mac PICT

Output:

BMP
JPEG
TIFF(no compression)
PNG you can free download MassConv 2.1 now.