Multiple file extensions in OpenFileDialog

Try:

Filter = "BMP|*.bmp|GIF|*.gif|JPG|*.jpg;*.jpeg|PNG|*.png|TIFF|*.tif;*.tiff"

Then do another round of copy/paste of all the extensions (joined together with ; as above) for “All graphics types”:

Filter = "BMP|*.bmp|GIF|*.gif|JPG|*.jpg;*.jpeg|PNG|*.png|TIFF|*.tif;*.tiff|"
       + "All Graphics Types|*.bmp;*.jpg;*.jpeg;*.png;*.tif;*.tiff"