The Pen Control has the Image property, which returns a URI string in the format of appres://blobmanager/<some numeric ID>/4 where the last number is an index for the image which is presumably stored in the local cache for the app. When the app is closed and reopened, any data URI referencing a previous index fails, so it seems that images need to be used within an app session otherwise they are lost.
This raises the question: how can the pen control image be saved while the app is running in offline mode?
Using SaveData and LoadData does not work, because the data saved only contains the data URI string and not the image, and after the app is closed and reopened, the data URIs are pointing to images which no longer exist in the local app cache.
Other suggested ways around this are:
Use the Import / Export controls - this exhibits the same behaviour as SaveData and LoadData
Use the Download function - this fails saying that the specified URI is invalid
So, how can the pen control image be saved and persisted over an offline session? Obviously, any solutions using Flow aren't workable, since they require online access.