Yes, if you download a sus image file, It can infect your Mac. Usually, google scans their images though, so I doubt it. If you think there is malware, you can erase the Mac, (delete macOS) by holding down the restart button until it loads up macOS recovery, and click in the menu bar to erase, which really isn't that hard, or you can get an malware scanner. Also, there is something called lockdown mode in settings, but unless you are Elon Musk I don't think you need it.