For optimal performance on Facebook ads, it's crucial to select image sizes that cater to various placements and devices. The 1080 x 1080 pixel (1:1 aspect ratio) square image is often considered the most versatile, performing well across Facebook and Instagram feeds, Marketplace, and Audience Network. For link ads that appear with a headline and description, a 1200 x 628 pixel (1.91:1 aspect ratio) landscape image is highly recommended, ensuring your visual is properly displayed. When targeting mobile news feeds or Instagram, using a 1080 x 1350 pixel (4:5 aspect ratio) vertical image can capture more screen real estate and attention. Furthermore, for full-screen experiences like Stories and Reels, a 1080 x 1920 pixel (9:16 aspect ratio) is ideal to fill the entire screen effectively. Ultimately, while these are recommended dimensions, testing different aspect ratios and sizes for your specific campaign goals will yield the best results.