## 2 Materials and Methods
### Protocol 1: Determination of Distance Limit of Target Detection  
\"Markers\" were fabricated from colored self-adhesive labels. Neon green or neon pink squares of three differing sizes (2 \(\times\) 2 mm; 5 \(\times\) 5 mm; and 10 \(\times\) 10 mm) were cut from self-adhesive label stock (Figure 2a). A single marker square was affixed to a flat wood stick as a single target (Figure 2b). A distance of 1 ft was then measured from the target and marked on the ground. The ground was marked at 1 ft intervals up to 20 ft away from the target. An Apple iPhone 8 (or newer version) was placed parallel to the target (handheld)-beginning 1 ft from the target and moved back progressively in increments of 1 ft up to 20 ft (Figure 2c). Photographs of an actual experimental setup and the accompanying raw data images are shown in Figure 3. At each distance a short video (5-10 s) was recorded of the image at 60 frames per second (fps) and in resolution of 1080p. At all times, care was taken to keep the phone parallel with the target and free of movement or vibration. The above sequence was performed for targets of each size (2 \(\times\) 2 mm; 5 \(\times\) 5 mm; and 10 \(\times\) 10 mm). All procedures for each target size were performed in triplicate. Video images captured at each distance increment were processed and results plotted. The end point \"distance limit of target detection\" was defined as the distance at which the MO\({}^{2}\)CA system could not detect or identify the target reproducibly, i.e., a cut off distance, after image processing\"Resolution\" was defined as the minimal size of a target at a given distance from the camera that could be detected by the MO\({}^{2}\)CA system. Figure 1: Flowchart depicting experimental protocols. Figure 2: Protocol 1: Configuration for single target resolution. Neon green or neon pink squares of three differing sizes (**a**). A single marker square was affixed to a flat wood stick as a single target (**b**). Measurements of 1 ft were marked from 1–20 ft, and videos were captured at each of the markers (**c**). (For representation purposes, the iPhone is shown in one hand, in the study two hands were used for stability). Protocol 2: Determination of Distance Limit of Target Pair Detection and Inter-Target Discrimination  
Markers were fabricated as in Protocol 1 (Figure 4a). Two marker squares of the equal size, i.e., a \"target pair,\" were affixed to a flat wood stick as a \"binary target\" at a defined inter-marker spacing of 2 mm (Figure 4b). Sequential video clips were captured at 1 ft intervals, as the smart phone was progressively moved back in increments of 1 ft to 20 ft (Figure 4c) as in Protocol 1. The above sequence was performed for each size marker target (2 \(\times\) 2 mm, 5 \(\times\) 5 mm, and 10 \(\times\) 10 mm). Note for the 2 mm marker the test range began at 0.5 ft extending to 20 ft, based on preliminary results indicating the utility of being closer to the camera. This process was repeated for each size marker target at inter-marker spacings of 5 mm and 10 mm as well. All procedures were performed in triplicate. Video images captured at each distance increment were processed and results plotted. The end point of \"distance limit of paired target detection\" was defined as the distance at which the MO\({}^{2}\)CA system could not detect or identify the target reproducibly after image processing. \"Inter-target discrimination\" was defined as the minimal inter-target spacing at a given distance from the camera that could be detected. Protocol 3: Determination of Distance Limit of Moving Target Detection and Resolution (Working Distance)  
For motion studies 10 \(\times\) 10 mm neon pink and neon green squares markers, fabricated as above, were used (Figure 5a). A neon pink marker was affixed to the free tip of the swing arm of a metronome. A neon green marker was affixed to the non-moving base of the metronome just under the swing arm, to indicate the origin of the swing and determine the radius (Figure 5b). The metronome was set at 96 beats per minute (bpm).