You cannot use JPG for POI Icon.
Use BMP (8 bits per pixel , 256 colours)
Size 24x24 pixels works for low resolution nuvi's and 3790
Size 48x48 pixels works for high resolution nuvi's (2012 series)
Transparent colour is Magenta RGB 255,0,255
JPG's can be embedded in TourGuides as well but I think the TourGuide will only work Properly in a Unit that has MP3 enabled.
The JPG will not display while driving but is viewable in Where To.
Below is an example that that has WAV BMP and JPG
It compiles correctly in POILOADER with SOX and WORKS on 3490 with MP3 enabled.
To test for your area just change the LAT LON but leave everything else the same.
The Filenames TourGuide is very important as it binds the WAV and BMP to the GPX, The JPG is called by the <link href="http://www.gpspower.net/C:/tourguide/One.jpg"/> in the GPX
You must use the folder c:\tourguide as the container for all the files.