Currently, when we save a Pen Input (in a Collection or Data base) it is saved in a format that prevent to do any modifications to it (appres://blobmanager/XXXXXXXXXX).
There is a way around by saving it to an excel sheet on One Drive which save the Pen Input as a PNG in a another folder.
But this work around is far from being ideal, and doesn't work if you don't have access to internet.
It would be great if we can choose the output format of the Pen Input directly in the App, either keep the blob storage or choose base64, PNG etc).
Updating status and adding @FilipK
Thanks @MSLtd for explanation.
My understanding is when you read the value of PenInput.Image property, it gives you the URI only which is a reference to BlobManager stored in the current session. This URI is the only piece of data can be saved locally using SaveData while you're offline. If your PowerApps app is closed down on your mobile device while you are still offline a new session will be started next time you open it and that URI previously saved locally is not valid anymore which means the PenInput data is lost.Is this also your understanding?