how I select multiple png images and convert it in one GIF image

If you want to turn multiple images into an animated gif you can try the command line tools that come with ImageMagick[^].

The following example will take all files ending in png from the current working directory and turn then into an animated gif:

> convert *.png animated.gif

[Edit]There seems to be a wrapper for .NET on codeplex: ImageMagick.NET[^][/Edit]

Regards,

— Manfred