Civitai now shows what image an image was remixed form in the image data.
Unfortunately, the implementation is pretty bad. There's no way, that I can find, to clear this status on older images. This makes it really weird for users who use and used remix on their own images to quickly restore a prompt skeleton (preferred checkpoint+generator quality settings+prompt that starts "official art, masterpiece, best quality, absurdres, very aesthetic, 1girl, solo, female focus" + their preferred negatives). Worse still, its also been silently collecting this data for at least 11 days. There's also a major bug related to content filters that I have no idea how it wasn't noticed.