
I've never touched pinterest before, I've only used it on twitter.
For twitter it works the following way:
-Right click on the field
-Set Value with the help of a macro: {-Directory.SubItem-|-C:\yoururl-|-f-|-true-|-12-}
f means file
true so the files are ordered alpabetically
12 the number of the item.
Let me know if this works
Easiest way is just to put the file path of a picture you have in the input box and then let zenno create the branch. When finished recording the template, go into the template editor and use your macro to pull the random file from the path as explained above.