Hello Jordy,
Does your Itemlist already have an Itempicture or not?
If it does already have Itempicture then you can do two things:
1. Retrieve the itempicture in your micro- nanoflow before the show page action and give this list as parameter
2. Removing the parameter from your page and retrieve it over association on your page, this is changing the datasource of listview itempicture from parametre to database over xpath
If you do not have itempicture yet or are not sure that you have them yet then you need to first create them in your microflow before you open your page. You can do this by creating a micro- nanonflow where you retrieve the itempicture and if it is not existing then you create it(also known as a fetch or create microflow), maybe you need to do this in a loop. because for every itemlist object you maybe need a picture.
Hope this helps,
Good luck
PS an example whereby an extra object is created before opening page you can find in the Administration module in the microflow NewAccount the password data is there created before you show the page