Here’s a standard USB webcam sitting on top of 30 meters of USB extension cables (three 10 meter cables). Three cables daisy chained together with the webcam attached to the end seems to be the functional limit. Adding a 4th 10-meter cable results in the camera not being recognized.
These 10 meter extension cables, also called “repeater” cables, are available for around $10 apiece. We’ve been using them to run a webcam out in the intertidal zone to watch limpets and snails crawl around all day and night.