How do I add Alt Text to images on my site?

[Pinksands]

I have built my site and am now trying to get it to come up in Search engines.
I want to add Alt Text to my images, how can I do this?

Thanks
Paddy

[travisamiel]

Also curious if it's possible to add this—especially to ensure accessibility!

[matthieudurey]

SAME :), I want ot know how to add Alt Text to images.