validate rule for the asset fieldtype do not work

[shabbarabbas]

if i set validation rules for the asset filed type like this

image_gallery: type: assets validate: required|image|mimes:jpeg,bmp,png display: Image Gallery instructions: Choose or upload an image for your Project, You can select multiple images up to 5. container: portfolio folder: / max_files: 5 restrict: true destination: assets/projects mode: grid
it keeps me giving error "The Image Gallery field must be an image.,The Image Gallery field must be a file of type: jpeg, bmp, png."
though i have select an image and it is png image

please help me how to setup the validation like image type or may be image min width or min height