  Conventional imaging at low light level requires hundreds of detected photons
per pixel to suppress the Poisson noise for accurate reflectivity inference. In
this letter, we propose a high-efficiency photon-limited imaging technique,
called first-photon ghost imaging, which recovers image from the first-photon
detection by exploiting the physics of low-flux measurements and the framework
of ghost imaging. The experimental results demonstrated that it could retrieve
an image by only 0.1 photon detection per pixel, which is three orders lower
than the conventional imaging technique. The SNR model of the system has been
established for noise analysing. Our technique is supposed to have applications
in many fields, ranging from biological microscopy to remote sensing.
