If images do not appear then your GD2 does not support the required functions to generate those captcha imaging.
As far as mobile that application as posted is basically very raw just a beginning. It may not work on all mobile devices properly. Viewing my sites look fine for how they are set depending whether they use or do not use the mobile thing on my motorola droid pro which is android system just fine. There will be lots of changes and updated and work considering mobile technology more forwards PP9. This is just a start and is subject to changes lots.
Just check in here for updates from time to time.