These days it's not uncommon for a typical family with a couple of kids in Junior School or higher to easily have in excess of 20-30 hours of video footage (still waiting to be edited) and several 1000 images. By the time your kids are ready to graduate it's a safe bet that you can double that - and at that size, chances are it won't all fit on your computer/s hard drive/s - which means you need a way to back up those files AND get them off your computer hard drive.
But first things first.
For storage of images and video you need to use a local computer hard drive, most likely the hard drive of your Mac. And to back this up you should use an external hard drive with Dropbox or Google Drive for everyday files, and Time Machine for everything else.
The problem comes when your local Mac Hard Drive is FULL, and you need to move that media off your Mac, just dumping onto an external drive is not good enough, as if that drive fails, (quite likely in my experience) you lose everything.
You can buy ANY Hard drive, they can all be reformatted on a Mac, using the Disk Utility Application, which will erase the drive and make it Mac (Mac OS Journaled), if you want to use it with Time Machine, or FAT 32 if you don't want to use it with Time Machine, and want to be able to read and write to the drive from a Mac or PC.
If you plug a brand new drive into a Mac, you should get a prompt from Time Machine asking you to format the drive automatically, all you have to say is YES!
If you do use a separate hard drive, make sure that you always have the data in TWO locations, otherwise it's not backed up, just moved. So if your Mac is FULL and you need to make space, this is not a good solution.
The solution for moving data off your HDD completely is to use a 'Hard Drive Enclosure' With a couple of Hard Drives plugged in.This is a 'RAID' set up: a Redundant Array of Independent Disks (redundant meaning, you can afford to have one fail without it being a problem) a big black box ($200) with space for 4 drives to slot in, each drive can hold about 1 TB or more depending on what you buy...
Back in 2013 I bought the Probox 4 Bay for $195, at Sim Lim Square (Best Bargain and I bought two 1.5TB internal drives to slot into it ($100 each), so I still have two spare lots for later expansion...
I make one drive copy the other, so I don't have to keep it on my Mac - remember if the data is not in two places it's not backed up!
Mine looks like this:
The process of copying that data from one drive to another can be done automatically, some of the more expensive solutions come with built in software that does this automatically, or you can just do it yourself, by copying data from one to the other manually, a bit tedious, but it gets the job done.
Drobo is a well known brand, well known by geeks anyway.
If you're happy to spend a little more money (this media is priceless after all) Consider a hybrid solution like Amazon S3, mostly because the NAS has integration built in and can use an existing normal amazon store account to manage the storage as well. I'm sure there are others, ideally you want a local, cable connected (reliable) RAID backup, combined with a cloud back up, this might be integrated into the RAID box, or you might set this up separately, see below:
A cheap/easy option is to use Google Photos, unlimited backup is free, but resizes the media, or pay a reasonable amount to store all your media online, without resizing...
If you install the desktop and iOS apps, it will automatically upload ALL your media to your Google account.
If you're confused about sizes of hard-drives, see my other post here. But a guide would be that each internal drive needs to be at least 1 Terabyte, so if you buy 2 you effectively have one, as the second drive is just mirroring the first one.