I think it is important that we all use the highest possible quality when investigating anomalies.
For the casual anomaly hunter, using Zoomify is the obvious way to go. Bear in mind that your browser does do some downloading, but you might find this is still a lot better than the alternatives. It’s obvious that magnifying a Zoomify screencap is not an acceptable way to post anomalies, but it’s a good way to find them… and you can still post unmagnified caps.
I will add this: Zoomify is extremely awkward to use most of the time when you need to locate a small feature… particularly when the IMG must be flipped vertically and/or horizontally to match the actual lunar landscape. As mentioned before, Zoomify does not correct the NAC’s to their proper orientation. I don’t know if this is intentional or not, but if the Zoomify people are reading this, this bug really needs to be corrected!