A square 1024x1024 digital painting, evoking a mysterious and slightly whimsical atmosphere. The central image is a close-up of a stylized, intelligent-looking frog wearing a small, classic detective's fedora hat tilted slightly. The frog's eyes are large and expressive, conveying curiosity and a hint of melancholy. Behind the frog, a subtle, out-of-focus background suggests a dimly lit, old study or library, with hints of shadowy bookshelves and perhaps a faint glow from an unseen lamp. The color palette should be rich and atmospheric, featuring deep emerald greens, muted browns, and touches of sepia, with soft, diffused lighting that creates a sense of depth and intrigue. The overall mood is contemplative and intriguing, suitable for a sophisticated mystery novel. The composition is centered on the frog's face, drawing the viewer's attention immediately. Professional audiobook cover aesthetic, square 1024x1024 format, no text.