Top: Mid-IR spectrum of faint LINERs (grey continuous line), SBs (green dotted line), elliptical galaxy NGC 1407 (cyan dot-dashed line), synchrotron emission of a jet (pink dot-dashed line), and ADAF (red dashed line). Bottom: Mid-IR spectrum of faint LINERs (grey continuous line), SBs (green dotted line), AGB star SMP SMC 018 (long-dashed blue line), post-AGB star IRAS 01005+7910 (dot-dashed orange line), and PN SMP LMC 79 (short-dashed red line).