Thanks a lot for your response. Indeed screen and image resolution correspond. As I needed a fast solution, I reduced my images to 844x641 in order for them to be displayed in an "image" item with a 1024x768 screen. With a black background and fixed duration, the black border isn't visible, I only have a black frame all around.
Hoping the next version will take into account the need for images to be displayed full screen easily.

Best,

Mathias Theunis