For　the　first　time,　we　study　the　fluorescence　signals　induced　by　spontaneous　emission　under　three　different　kinds　of　atom　densities　(including　proper,　high,　and　low　atom　densities).　Apart　from　the　fluorescence　signal,　we　also　present　the　characteristics　of　images　and　spectral　signals　of　the　probe　transmission　and　four-wave　mixing　under　proper　atom　density,　such　as　the　Autler-Townes　splitting　of　the　spectral　signals　and　the　images.　In　addiiton,　under　other　two　improper　atom　densities,　we　give　the　observations　of　spectral　signals　of　two　super-fluorescence　signals　to　understand　the　different　contributions　of　high　and　low　atom　densities.　The　phenomena　in　spectral　signals　and　images　can　be　well　controlled　by　adjusting　the　incident　beam　powers　and　frequency　detunings.　Such　studies　can　be　used　in　all-optical　controlled　spatial　signal　processing.