A Lothian agricultural college is investigating a "beautifully executed" crop circle which appeared in its grounds overnight.
The 30ft-wide circle is a depiction of the logo belonging to Oatridge College in West Lothian.
It appeared in a remote field on the Oatridge estate on Wednesday.
Crop circles are most often found in fields of standing cereals. The Oatridge circle is believed to have been burned into grass using chemicals.
Farming experts at the college said they were "baffled" as to how it was completed in secret.
Agricultural lecturer Joy Miller said: "It's beautifully executed and the circle is perfectly round."
She added: "We think that it's a student prank using some sort of weed killer, but the surprising thing is that on a campus swarming with students, there hasn't been the slightest whisper about who did it or how it got there.
"The closest thing we have to evidence is a couple of reports of lights being seen during the night in the general direction of the field.
"That makes it even more remarkable that someone could replicate the college logo so accurately, if they were working by torchlight in the dark of the countryside."
Oatridge is Scotland's largest centre for education and training for a range of rural and land-based industries, and caters for more than 3000 students every year.