I was issued a chromebook, as was everyone at my school, to use for work in class and in case school has to shut down again. We bring it home so it connects to my personal Wi-Fi when I'm at home. I was working on homework and needed to transfer a pdf file off of my tablet to my chromebook, so I decided to just hook it up via USB. Could the school see all my files and pictures when it was hooked up even though I'm on my Wi-Fi? Are the files on my tablet no longer visible on the chromebook once the USB connection is unhooked?
If they just gave you a stock computer without any modifications, probably not. Usually computers do not automatically make a copy of data from USB drives. However it is not uncommon to store metadata about the files somewhere, for example thumbnails and things like what sort order you picked for that drive. Usually the natural place to store this is somewhere in the same directory, so there's not really information being extracted from your drive. But depending on how exactly the computer is configured, some references may remain on the computer even after.
For example, if you open any files they will probably be recorded in some "recently opened files" menu that will remain even after the USB drive is gone. This will only record the name of the file, not the contents, though. You could simply avoid opening your photos, but it's possible that you have some kind of image browser installed that automatically scans every directory and saves thumbnails elsewhere.
Of course the school could have installed some kind of program that does record some or all of data from USB drives. It may be unintentional, such as an antivirus that collects files it consider suspicious (false positives are very common). Or it may be intentional, if the school IT wants to monitor what students are doing "for their security". Furthermore, the computer may be compromised by hackers, malware or viruses, who install evil software without the school's knowledge.
In practice it is rare for schools to spy on their students in such a blatant way (although it's not unheard of), and from what I know Chromebooks aren't considered particularly insecure (if you trust Google...). But there's also no guarantee that it won't happen. The safest option is:
- Use your school laptop strictly for schoolwork
- Never login to any personal account or enter any personal password on the school laptop
- Never let any private files come on to the computer or touch it in any way
- Assume someone is watching everything you do on the computer at all times, and will keep a copy of everything you do on it
By this token, I would never plug in a USB drive with personal photos to a school laptop. I would do a secure erase of the whole drive before and after it touches the laptop, or more conveniently just buy a separate USB stick for school stuff (they're like $10).
In principal, the school (or school employee) could have installed any kind of spying software on your chromebook, but this requires from them skills, effort and motivation. Yes, potentially they could have read all the files from the tablet, though that would require some determination. I'd like to say it's unlikely for a typical school to do it, but I can't be sure.
Once you disconnect USB the chromebook should not be able to read files stored on the tablet just because they are in the same WiFi, unless there are some issues with security of the tablet.
If you're concerned about your privacy, look for ways to transfer only the specific file you want to send. E.g. share this file in google drive or similar service. Additionally, don't use the chromebook for private activities: don't log in to your private accounts (social media, e-mail, file storage), don't view webpages that you wouldn't like your school know you're viewing, don't write things that you'd prefer to keep secret, be careful about what the camera and microphone can record etc.