The upconversion infrared (IR) image sensor selectively emits visible light photons from the regions that have absorbed IR photons, allowing for simplified manufacturing without the need for complex pixel integration. These pixel-less upconversion IR image sensors enable low-cost, nondestructive imaging in the Internet of Things, security, and bioimaging applications, which include identifying blood circulation, tumors, and vascular structures. Here we designed the material and structure of a quantum dot upconversion IR image sensor (QUIS) and achieved a photon-to-photon efficiency of 982% by inducing photomultiplication. A QUIS, designed with an inverted structure for charge balance, uses Mg-alloyed ZnO nanoparticles as an electron transport layer to control the electron–hole ratio. We analyzed the type and amount of charge present within the QUIS, elucidating the mechanism driving photomultiplication and the origin of photon-to-electron efficiency exceeding 100,000%. The pixel-free QUIS is demonstrated as a bioimaging sensor by detecting human movement and blood pulse detection.