SamMobile outed the image and cites an inside source claiming the Android handset will feature a 4.99-inch Full-HD display and a smaller bezel than the Galaxy S3.
The authenticity of the picture is uncertain, with the report noting a resemblance to the existing Galaxy S3 and Galaxy Premier handsets and suggesting it could be a render.
Previous rumours suggested that the Galaxy S4 will feature a powerful quad-core processor, a 5-inch 1080p display and a 13-megapixel camera.
The exact launch window for the Galaxy S4 remains unclear, with sources suggesting that the Korean tech giant is planning to hold a dedicated media event around April to unveil the phone.
Samsung's Galaxy S4 is expected to compete with Apple's current generation iPhone 5 and its successor, as well as other high-end Android devices and Windows Phone 8 handsets.