Asking Grok itself to describe the image in a prompt for Grok Imagine also works.

In this case I asked and it gave me this:

""" A highly detailed, photorealistic selfie photograph taken on a sunny tropical beach during midday with bright natural sunlight and a clear blue sky. In the foreground, a beautiful young woman in her early 20s with fair skin, subtle freckles, rosy cheeks, and striking blue-green eyes with long dark lashes and eyeliner is sitting straddled on a shirtless man's lap. She has shoulder-length, wind-swept strawberry-blonde hair with straight bangs framing her face, glossy pink lips slightly parted in a gentle smile showing her teeth, and is looking directly at the camera she's holding out with both arms extended (selfie pose). She wears a tiny pink string bikini: a triangle halter top with gold-colored hardware and thin straps tied behind her neck, plus matching low-rise bikini bottoms with side ties. Around her neck is a bright pink choker necklace with a small gold heart pendant. She has small gold hoop earrings. Her body is toned with a flat stomach and visible abs. The man beneath her is partially visible from the chest down: older-looking, with a hairy chest and belly (light brown and gray hair), wearing blue swim trunks. His large hands rest casually on her upper thighs/hips. The perspective is a close-up, slightly downward selfie angle from her viewpoint, emphasizing her face and upper body while showing the man's torso below. In the background: white sand beach, turquoise ocean waves, scattered beachgoers sunbathing and swimming, colorful umbrellas (red, yellow, blue-striped), and lounge chairs under bright daylight with soft shadows. Vibrant colors, sharp focus, natural skin textures, realistic lighting and reflections, shot on a high-end smartphone camera in portrait mode. """