From an article by David Prudames, published on www.24hourmuseum.org.uk:
Using laser scanning technology to study Europe’s most famous ancient monument, a team of computer experts and archaeologists has discovered carvings of two axe heads on Stonehenge.
The most hi-tech investigation of the monument to date, the study was carried out between 2002 and earlier this year by a team from Wessex Archaeology and Archaeoptics Ltd.
Although similar carvings were first found at Stonehenge 50 years ago, they have never been fully surveyed or studied.