Things to look for on cdv images is the clarity and color of the image. Under magnification it should be smooth gradual transitions between items. Modern ones are sometimes so poorly done that they have dots that make up the image or the tinting is off. Some bad fakes have a strange look from printers blurry or off colored. Paper used to make the stock card should usually have fibers in it so you see lines. Little brown dots like foxing are sometimes but not always an age indicator. The cdv's that have typed words on the bottom are usually later or copies. An image like you have is rare and commands large sums for battlefield flags.
Ooh, this made my heart skip a beat! Pretty sure it's authentic. The wear patterns and color all check out. You'd want to look at it under magnification, as the earlier posters have rightly said but . . . dang!