restrict file type for ContentReference property

Is there a way to only allow specific file types in the ContentReference property? For example below, I only want to allow JPG and PNG, no GIFs (even though GIFs are allowed elsewhere on the site.

        [CultureSpecific]
        [AllowedTypes(typeof(ImageFile))]
        [Display(
            Name = "Image",
            GroupName = SystemTabNames.Content,
            Order = 30)]
        public virtual ContentReference Poster { get; set; }

[Pasting files is not allowed]