When creating an event for your author giveaways, check out these tips for your images.
Book Giveaway Event Image Size
Add an image to represent your event. This appears as a banner at the top of your event page.
Recommended size: 1180 × 380 (max400px) (landscape format)
Accepted formats: PNG, JPEG — maximum 2MB
Keep all important text and imagery centred, as the edges may be lightly cropped on some screens. A landscape photo, a book cover adapted to landscape, or a purpose-made banner all work well at this size.