Nowadays, the number of visible physical devices exposed on the Internet is dynamically increasing and they play a crucial role for bridging between the cyber space and the physical world, such as network printer, Webcam, and industrial control devices. Discovering these devices brings about the deep understanding on these devices' characteristics and help secure device security in the cyber space. A device fingerprint is a prerequisite of device discovery in the Internet. However, today's online device search depends on keywords of packet head fields and the keyword collection is done manually. This impedes an accurate and large-scale device discovery, due to high human efforts and inevitable human errors, as well as the difficulty of keeping keywords complete and updated. To address this problem, we propose GUIDE, a framework to automatically generate device fingerprints based on webpages embedded in these devices. In order to demonstrate how GUIDE works, we also develop its prototype system and provide a case study which discover surveillance devices in the cyber space.