Hi
Good call - see "iCloud is not a backup" below
Time machine is the best way in my opinion. Get a hard drive with enough space (At least 2, preferably 3 times the size of the data you want to back up). Plug it in and set time machine to backup to it. By default it doesn't backup external drives: you will need to specifically tell it to include the hard drive with your photos on in the backup, in time machine options:
https://support.apple.com/en-us/HT201250
Time machine keeps hourly backups for a day, daily for a month, and monthly backups until the drive fills up, at which point the oldest backup gets deleted. It is fully automatic and wonderful. The only thing you need to worry about is the backup drive needs to be connected to your mac as much of the time as possible. Not a problem for a desktop machine, but if a laptop, you need to leave it switched on somewhere with the backup drive connected long enough for the backups to take place.