A row has erupted over a woman''s claim that her junk-shop canvas is by the world''s most expensive artist. Louise Baring reports

In pictures: the world''s most expensive paintings

Tomorrow night, Teri Horton, a 73-year-old former long-haul truck driver from California, will star on David Letterman''s Late Show ¨C one of America''s best-loved television programmes ¨C telling viewers about her unlikely thrift-store find: a large-scale drip painting by the American abstract expressionist Jackson Pollock, the world''s most expensive artist.