With photomanipulation two points come to mind:

The work involved in manipulating the image is the work (generally) - thus is it the manipulation which needs to be done in the timescale, or do you have to take the photo's as well in that timescale?

Semi-related to the above: Does it have to be your own photography entirely? (a lot of manips i have done used free stock images)

Obviously these Q's are only really applicable to the current challenge.

I can see the benefit of the idea of the date/exif condition, it will force people to think about the challenge when out shooting during the month :) Nice job on implementing that!

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography