We'll give you a clue: It was taken in full daylight with the use of a telescope on July 8th, 2013 at exactly 7:14 UTC.
The extremely thin arc that you see here is the tiny lunar crescent at the precise moment of the New Moon. In other words, it's the youngest possible crescent. The age of the Moon's cycle at this instant is exactly zero.
Image credit: Thierry Legault. Republished here with permission.
The lumps and bumps in the crescent, along with the gaps, are representative of the Moon's topology as seen from this angle (i.e. mountains and craters) — which should give you an indication of just how remarkably thin this arc really is.
The record setting image was taken by Thierry Legault from a shooting site in Elancourt, France.
"At this very small separation, the crescent is extremely thin (a few arc seconds at maximum) and, above all, it is drowned in the solar glare, the blue sky being about 400 times brighter than the crescent itself in infrared (and probably more than 1000 times in visible light)," he writes on his website. "In order to reduce the glare, the images have been taken in close infrared and a pierced screen, placed just in front of the telescope, prevents the sunlight from entering directly in the telescope."
The New Moon is defined as the instant when the ecliptic geocentric longitudes of the Moon and the Sun are equal. It's the moment when the imaginary line joining the Moon and the Sun is perpendicular to the ecliptic (the plane of the Earth's orbit). It can also be said that it's the instant when their angular separation is minimum.
All images via Thierry Legault.