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"