The polarization of the conical electromagnetic radiation produced by the scattering of surface plasmons by film roughness in the Kretschmann attenuated total reflection configuration was measured. The conical radiation was p polarized in the plane of observation. A tip of a scanning tunnel microscope was brought close to the film surface to act as a plasmon-scattering center. From a measurement of the conical radiation generated by this single-scattering center, it was found that plasmons tend to be forward scattered. Using a scanning plasmon optical microscope (SPOM), we imaged plasmon-scattering surface irregularities, which act in a first approximation as independent conical centers, along with interferences caused by these fixed conical radiation centers and the moving conical radiation center (the SPOM probe tip). The possibility of detecting localized surface plasmons with a SPOM is discussed.