Note by @fastfinge

@the5thColumnist @RachelThornSub My suggestion would be to keep it simple. If the reason you posted the photo was because it was a pretty flower, well...that's fine for the alt-text. No matter how many words you use, you might not be able to communicate the exact feeling of beauty you experienced. If you could, you'd be a writer, not a photographer. Ask yourself why you posted, and what you want someone to take away from it. If you want them to notice the colour, or the size, or whatever, those are what goes in the alt text.