An image to be used as the start frame of the generated video. Requirements: 1. Only accepts 1 image; 2. Only supports two-person photos; 3. Better results when two people stand side by side at a moderate distance, showing from legs up; 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.