An image to be used as the start frame of the generated video. Requirements: 1. Only accepts 1 image; 2. Supports single-person, pet, two-person, or group photos; 3. Best for front upper body shots above waist, with subjects standing side-by-side for groups; 4. Images can be provided via URLs or Base64 encode; 5. Supported codecs: PNG, JPEG, JPG, WebP; 6. Image aspect ratio must be less than 1:4 or 4:1; 7. Maximum file size: 50MB; 8. Base64 decode length must be under 50MB with appropriate content type string.