I am by no means an expert with OLP but I do not think this is possible.
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However, if this is a one off thing you want to do here is a work around. You can link audio to a song. So here is what you could do.
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1. Create a Theme with the image you want to use and when you do that set the footer font size to 0.
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2.Then create a new song. OLP won't let you create a blank song so you will have to give it a name. I would suggest that you name it starting with the letter Z so it appears at the bottom of your song list in Media Manager, and also something to do with your image like ZSunset. It will also ask you for an Author and a verse. You can put in a single letter for the author and add a verse with some blank spaces. Set the theme to the theme you created with the image you wanted to use. Then use the Linked Audio tab to add your music and then save.
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3. Set your Settings>Configure OLP>Theme setting to Song Level.
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This isn't a clean solution but it will get an image on the screen with an audio track playing.