It seems the default ppcpictures screen has no picture category in it. A quick look through the skins on this forum reveals that none of the heavy hitters among the skin engineers use a ppc
You can just add one using the skin editor. Goto screen - select ppcpictures. Screen tab - Add category tab - type pictures and Create Custom Category. You should see a text listing of all your pics. Now on the Edit Category tab you can adjust it to suit yourself - tick Enable in the thumbnail section to show the pics.
Here's the contents of a simple ppcpictures.xml that should do the trick.
<?xml version="1.0" encoding="UTF-8"?>
<skin background="">
<skinsize>1360,768</skinsize>
<eventbutton>
<imagename>ppcblue.jpg</imagename>
<location>0,0,240,320</location>
<navitem>True</navitem>
</eventbutton>
<eventbutton>
<imagename>pictures</imagename>
<location>1,37,238,280</location>
<navitem>True</navitem>
<font>arial,15,regular</font>
<type>category</type>
<database>pictures</database>
<display>%display%</display>
<details></details>
<defaultlisting>False</defaultlisting>
<ratio>1:1</ratio>
<columns>4</columns>
<overlay>missing</overlay>
<layout>bottom 1</layout>
<scroll>Left Right</scroll>
</eventbutton>
<eventbutton>
<eventid>goto:ppc menu</eventid>
<imagename>back.png</imagename>
<location>4,1,35,35</location>
<navitem>True</navitem>
<font>Arial,9.99999999999997,regular</font>
</eventbutton>
</skin>
This works for me.
Looks like there is a problem in that tapping the pic on the ppc blows it up to full screen on the client but not the server, even when mimic is on. You'd need a pictureviewer screen (see Jowaldo's excellent skin for an example). I seem to recall people mentioning this before - maybe a feature request.