It would be nice (IMHO) if it were possible to get an image (either a jpeg or a png) of a whole webpage, not just of the part that is being displayed on the screen. AFAIK this is not possible yet.
Taking a screenshot OTOH is already possible: there are several options for this.
I know the size of such an image can be enormous. Maybe an upper limit would be useful: e.g. 100Mbytes. And yes, I know: a 100Mbyte jpeg is huge