The watermark is configured in the back office's watermark settings, with one checkbox per preset family ("Apply to automatic replacement families", product_card, product_page, category_banner, manufacturer_logo, mobile_thumbnail) rather than a single site-wide checkbox. The goal: only watermark the families that actually need it.
The common trap: checking every family out of reflex, including manufacturer_logo (brand logos, rarely proprietary visuals worth protecting) or mobile_thumbnail (thumbnails too small for a watermark to stay legible or dissuasive). Each extra checked family is one more variant to generate and cache on first visit, with no real protection gain on those families.
The practical recommendation: watermark product_page as a priority, the large-format image, most likely to be copied or republished elsewhere, and possibly category_banner. Leave thumbnail families (product_card, mobile_thumbnail) unwatermarked, since those are the ones appearing in dozens of copies per category page, where the cumulative generation cost is felt the most.
On the performance impact: the watermark applies when the variant is generated (first visit only, like everything else in ImagePipe), not on every display. Once cached, a watermarked image doesn't cost more to serve than one without. The real cost to watch isn't display speed, but the number of unnecessarily checked families.