This looks like a modern image although it's possible it is a high res scan of an older 35mm slide. It certainly looks like someone wearing what looks like an Autavia. The helmet looks authentic as Seppi only wore one style; the red with white Swiss cross and white stripes on either side of the cross. The person in the photo is also wearing a ring and it appears to be similar to the only ring he wore, a trophy of his win of the Mediterranean Grand Prix at Enna in Sicily in 1964. The win was so special to Siffert in that he beat Jim Clark narrowly.
It's also possible it might be his son, Philippe, who has driven one or more of Seppi's cars in historic events. Sure looks like a Porsche 908 in the photo. Without seeing his face in the image, it will be a mystery, for sure. Thanks for sharing!
Bob Keller