This article is showing you how to avoid the error “Image file xxxlogo.png is a default image” when publishing the Windows App Store.
The first thing you do to learn to create Windows App Store application is that, once you completed downloading any sample from Microsoft website. You must first replace all the logo by your own image.
Capture or create an image file with the size around 800 x 800 pixels then you will be safe. You can then resize it into 30×30, 50×50, and 150×150.
I zipped the sample image defaultmagepicture.zip and post in my public Onedrive. You might try to get it there.
Microsoft should not give this type of message without any explanation.