There has been some misunderstanding about the use of Picture Postcards in Open Philately, both among judges and often questions for clarification in seminars.
I thought it might be useful to ask the Bernard Jimenez, FIP Board member and Chairman of the Working Group who drew up the Open Philately Guidelines. He replied very clearly: “Picture postcards are non-philatelic material and count as such on Open philately.”
To summarise, an Open Philately exhibit must have at lest 50% philatelic material, which includes any item that is permitted in any other class or category, while the non-philatelic material may include up to 50%.
For further details, please see the FIP website with the brief, easily accessible 3-page guidelines. https://www.f-i-p.ch/regulations/