Pocketbook Era lockscreen / standby image

Currently, whenever you lock the screen, it gets little silly image on top of any contents (attached)

Is there a way to change it to any sort of full screen image?

I've looked all over the ini and cfg files in 'system' folder, but haven't found this exact image

Also, I'm not talking about Off / On images, those are easy to set up, it's the lockscreen image that I need to change :help:

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