It all depends.
1. What format are you shooting your pictures in?
I for example use JPEG for many of my pictures and the resolution is 3596 x 2492 for an example of one folder I have (4k is 3840 x 2160), this is about 1,200 pictures totaling around 2GB of space.
if we use this example then 12 TB (10.9 TB Formatted)
Well we have to do some math, as 10.9 TB = 10,900 GB
Next 1,200 pictures averaging 2 GB, lets multiply that, so 2,000 GB would give us
1,200 = 2 GB
2,400 = 4 GB
4,800 = 8 GB
9,600 = 16 GB
19,200 = 32 GB
38,400 = 64 GB
76,800 = 128 GB
153,600 = 256 GB
307,200 = 512 GB
614,400 = 1,024 GB
1,228,800 = 2,048 GB
2,457,600 = 4,096 GB
4,915,200 = 8,192 GB
at this point you have about 2,708 GB of storage which would allow you another 2,560 GB a total of 10,752 GB which about completely fills the 10,900 GB formatted space on a 12 TB drive. So after all this your answer is this;
using near 4k JPEG pictures on a formatted 12TB drive you could fit about 6 million 451 thousand 200 hundred pictures.
6,451,200 Pictures, now if you up the picture quality to PNG and higher resolution (let's say 4 times higher) you could still fit 1,612,800 UHD pictures.
Now if you want to compare video, 4k UHD video is about 6 GB for 1 minute, so do the math and you can se how much stuff you can actually fit on this 12TB drive
Well I have spent an hour and a half looking this up, double checking, and doing a quick 4k video to see if I average the same numbers that Digital Trends did, and I did so the numbers are solid Linda.
My recommendation is to buy at least two of these drives and keep a exact copy on the 2nd drive as these larger drives tend to have a higher failure rate then smaller drives did 10 years ago, just go to BackBlaze and check their top 13 most high failure rate drives
Join my YouTube channel at Milohajek and give me ideas on what you want to see as I have over 32 years of IT, network, system building and telecom experience and I enjoy sharing my experiences