To visualize the photos automatically using GnuPG on Ubuntu you need to edit your config file.
If you want to enable the exhibition on key listing look for and uncomment
# Display photo user IDs in key listings
# list-options show-photos
If you want to enable the exhibition on verification look for and uncomment
Add this to the config file with the photo viewer that you want to use. In this case eog
photo-viewer "eog %i"
Save the file, and enjoy.