Best device to store pictures from a computer and easiest way to do it?

I have an imac and its from 2011, just the other day it started just restarting or powering off on its own. I have a bunch of pictures of my kids from the past years and need to save them. Most of them are on Nikon Transfer from when I uploaded them from the memory card.

Added (1). fyi: i'm afraid it will just power off and not turn on so i want to save the memories.

External hard drive… Cheap and have lots of storage.

https://www.amazon.com/...00H4YGR48/

Burn to CD or DVD.

Ok, you have several different options here. Each has it's pro's and con's. Option 1 get and use a Flash Drive AKA a thumb drive. Ease of use and portability. Fairly low priced storage. Bad-when they fail it is usually very sudden. Backward compatibility is some what hit or miss. Average lifespan 5 to 10 yrs. Next option 2- External AKA Backup drive. Advantages- fairly easy to set up. Backs up all files automatically not just your photos. Somewhat portable. Cost is fair. Bad- Failure can be sudden. Average lifespan is the same as regular hard drives 3-10 yrs. Option 3 Disc storage (Blue Ray, DVD, CD) Advantage- Long shelf life 30+ yrs if maintained in proper environment (No direct sunlight, temps below 150 degrees). Somewhat easy to make/use. Ease of portability. Please note this is the method Films are being preserved as in a digital copy on a server and a Disc (Blue Ray) as a backup. Bad- Being phased out of standard Computers. You can add one externally. Finally option 4- Cloud storage Advantages- Can be set to backup all files regularly. Nothing to buy. Ease of access. Some are free up to a certain GB limit. Bad- If server is down no access. Depending on the users end agreement they may own your files, have access, ownership after death, etc. Servers subject to hacking. (All data centers are nothing more than servers with huge amount of storage capability) Personally I have a DVD burner (mainly pics and music and certain important Doc files) A backup drive for back up of all files every night. With a flash drive for important files like dog pics (lol) and about 600 books. Plus this has the advantage that there's no way I lose my files unless the entire house burns down and then I have my Disc's stored in a separate location.

"I have a bunch of pictures of my kids from the past years and need to save them."

In truth, your question is simply "What's the best backup medium?" because every type of file needs the same consideration, photo or not.

DO NOT use a thumb drive; it's not very reliable.
DO NOT burn files to a CD or DVD; all optical discs deteriorate in time, even if they may last 10-15 years. They are also easily damaged.

There are only two reliable options:

External drive (HDD or SSD)
Website, a.k.a. "cloud" (such as iCloud or Google Drive)

For my backups, a couple of 3.5 inch hard drives serves the purpose. In case of some hardware fault (drive motor fails), a lab can open the drive and possibly recover all data from the discs inside. This is much more likely to happen with the larger form factor than with teentsy 2.5 inch drives.