You will get the best results if you choose a high-resolution image (for example, 5000 x 3000 pixels). The upload module also signals when you are working with images/photos with too low a resolution. You can then use the photo on the panel but the result may be disappointing. If you do not have a suitable photo at a high resolution then you can also create a nice photo collage, where the different photos can then have a lower resolution.