How to get scale bar for brain MRI images downloaded off openneuro (.nii.gz files)

Hi - I’m Cary Leung. I am an associate professor at Widener University in the Department of Biology.
I’m developing a lab to study anatomical differences in brain structures using MRIs. I am hoping to learn from someone about how to get accurate measurements on MRIs (like an accurate scale bar).
My colleague shared this wiki page FSL - FslWiki but I haven’t been able to find a program that does what I want (scale bar for .nii.gz files)
If anyone here can provide any guidance I’d appreciate it!
Thank you in advance!

You might find some useful plotting tools in Nilearn (e.g. this function). The website has a lot of documentation and tutorials for plotting images with colorbars.