In general, the resolution and aspect ratio of the images you upload should match the resolution of the TV you'll be showing your Display or Slideshow on.
Some common sizes include:
Size | Resolution (W × H, px) |
1080p HD (Standard) | 1920 × 1080 |
1080p HD (Portrait / Rotated) | 1080 × 1920 |
4K UHD (Standard) | 3840 × 2160 |
4K UHD (Portrait / Rotated) | 2160 × 3840 |
8K UHD (Standard) | 7680 × 4320 |
8K UHD (Portrait / Rotated) | 4320 × 7680 |