Image-to-video works from the visual decisions already present in the source. The character design, crop, pose, lighting, background, and color palette all become constraints. If the still image is confusing, the motion brief has to spend its limited attention repairing the frame before it can animate it.
Use a clean JPG, PNG, or WebP with one readable subject and enough space in the direction of travel. Check the face, hands, costume edges, and small accessories before upload. Animation tends to make existing ambiguities more visible, so correct the still first when a detail is essential.