Hey Poussin,
You bumped into a boundry of LabVIEW PDA. LabVIEW PDA did not support custom controls at all uptil very recently. Only since LV PDA 7.1 there are a few features which are possible like coloring and resizing, see the link below.
http://digital.ni.com/public.nsf/websearch/08DD9CAACA1F64F586256E920061E4CD?OpenDocument
Using pictures however is not possible. The control will have its functionality on the PDA but it will not show its decoration.
Regards,
Wouter
National Instruments