Test was done with 3 Mapserver versions: 5.2.0, 5.2.1 and 5.3-dev. Two first 
were form MS4W installations, dev version from FWTools package.

If there are no OUTPUTFORMAT sections in the mapfile, Mapserver is advertising
in the getCapabilities document the the following image formats are supported:

   <Format>image/gif</Format>
   <Format>image/png</Format>
   <Format>image/png; mode=24bit</Format>
   <Format>image/jpeg</Format>
   <Format>image/vnd.wap.wbmp</Format>
   <Format>image/tiff</Format>
   <Format>image/svg+xml</Format>


However, two of these formats (image/png; mode=24bit and image/svg+xml) 
do not produce an image but just an error.Here are mapserv -v listings 
for each version, and corresponding lines from ms errorfile.


D:\Program Files\ms4w\Apache\cgi-bin>mapserv -v
MapServer version 5.3-dev OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP 
OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=FREETYPE SUPPORTS=ICONV SUPPORTS=WMS_SERVER 
SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT 
SUPPORTS=WCS_SERVER SUPPORTS=SOS_SERVER SUPPORTS=FASTCGI 
SUPPORTS=THREADS SUPPORTS=GEOS INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE

[Tue Mar 17 13:54:58 2009].312000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 13:55:12 2009].649000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 13:55:25 2009].813000 msWMSLoadGetMapParams(): Image handling error. Unsupported output format (image/png;).
[Tue Mar 17 13:55:36 2009].977000 msDrawMap(): Layer 0 (kaikki), 0.016s
[Tue Mar 17 13:55:52 2009].643000 msDrawMap(): Layer 0 (kaikki), 0.032s
[Tue Mar 17 13:56:04 2009].134000 msDrawMap(): Layer 0 (kaikki), 0.016s
[Tue Mar 17 13:56:15 2009].782000 msWMSLoadGetMapParams(): Image handling error. Unsupported output format (image/svg xml).



D:\Program Files\ms4w\Apache\cgi-bin>mapserv -v
MapServer version 5.2.0 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP OUTPUT=PDF
 OUTPUT=SWF OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE 
 SUPPORTS=ICONV SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT 
 SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER SUPPORTS=SOS_SERVER
 SUPPORTS=FASTCGI SUPPORTS=THREADS SUPPORTS=GEOS SUPPORTS=RGBA_PNG 
 INPUT=JPEG INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE
 
[Tue Mar 17 14:00:04 2009].44000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 14:00:19 2009].766000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 14:00:30 2009].409000 msWMSLoadGetMapParams(): Image handling error. Unsupported output format (image/png;).
[Tue Mar 17 14:00:39 2009].504000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 14:00:59 2009].836000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 14:01:08 2009].166000 msDrawMap(): Layer 0 (kaikki), 0.016s
[Tue Mar 17 14:01:21 2009].122000 msWMSLoadGetMapParams(): Image handling error. Unsupported output format (image/svg xml).


D:\Program Files\ms4w\Apache\cgi-bin>mapserv -v
MapServer version 5.2.1 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP OUTPUT=PDF
 OUTPUT=SWF OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE SUPPORTS=ICO
NV SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER
SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER SUPPORTS=SOS_SERVER SUPPORTS=FASTCGI SUP
PORTS=THREADS SUPPORTS=GEOS SUPPORTS=RGBA_PNG INPUT=JPEG INPUT=POSTGIS INPUT=OGR
 INPUT=GDAL INPUT=SHAPEFILE
 
[Tue Mar 17 14:08:37 2009].417000 msDrawMap(): Layer 0 (kaikki), 0.031s
[Tue Mar 17 14:08:51 2009].480000 msDrawMap(): Layer 0 (kaikki), 0.015s
[Tue Mar 17 14:09:04 2009].856000 msWMSLoadGetMapParams(): Image handling error. Unsupported output format (image/png;).
[Tue Mar 17 14:09:15 2009].28000 msDrawMap(): Layer 0 (kaikki), 0.015s
[Tue Mar 17 14:09:23 2009].310000 msDrawMap(): Layer 0 (kaikki), 0.016s
[Tue Mar 17 14:09:31 2009].716000 msDrawMap(): Layer 0 (kaikki), 0.016s
[Tue Mar 17 14:09:43 2009].544000 msWMSLoadGetMapParams(): Image handling error. Unsupported output format (image/svg xml).