  Arbitrary Nth-order ($N\geq2$) lensless ghost imaging with thermal light has
been performed for the first time by only recording the intensities in two
optical paths. It is shown that the image visibility can be dramatically
enhanced as the order N increases. It is also found that longer integration
times are required for higher-order correlation measurements as N increases,
due to the increased fluctuations of higher-order intensity correlation
functions.
