Adding photos to POI files

Yep, you can add photos to POI files. Check out Extra POI Editor. Its freeware (create by TurboCCC, a member on this site) which allows you to easily create POI files.

http://turboccc.wikispaces.com/Extra_POI_Editor

I believe that you will have to use the TourGuide form of a POI file in order for the pictures to show.

Look at Help in POILoader (search for TourGuide) for more info.

with a Nuvi 1350 and I add a picture (jpg) to caches that may need some extra attention (i.e new area to me and parking). Here's an example of gpx coding: Note the the real coding uses <> rather than square brackets.
[link href="file://C:/Garmin/_upload2garmin/GC28CVG.jpg"/]

I am using it successfully on my GPX files for county court-houses in Tennessee. It works great. I downloaded pics from the internet and saved them.
On my file, the first POI has this in the Browse window.

I do not use Tour Guide.
I will replace these pics with my own after my vacation next April.

I use the GPX editor to associate images with POIs. I had a list of my offices and linked a photo of the office to aid in locating it once I arrived at the address. It works like a charm!

http://geepeeex.com/

The .gpi file will be larger (sometimes considerably) depending on the resolution the images were taken at.