This is awesome. I have had the problem that og-image/meta tags are such a hassle (not hard, but just a hassle) -- and was really putting together an idea of making it easier (also supporting SERP previews) and via a JS script. It would use a dashboard so that you didn't have to update the code. But this is definitely one step closer to never having to worry about og-meta tags again :)
Question: I scanned through the landing page but didn't really see any examples of the watermark. Is every og-preview image watermarked?