Alt text aren't detected – SEO

I’ve added alt texts to images showed in my blog (Blogger):

<img alt="lune insomniaque" height="424" src="https://3.bp.blogspot.com/-2mKhLneD2QY/V0GeFfPnyuI/AAAAAAAAAAM/IJdyY4wmKoshK50OtSQW9eR_6fBCD1tXACLcB/s640/moon-1054721_1920.jpg" title="La lune, le quotidien des insomniaques" width="640" />

but when I’m using various SEO tools it says me that there are no alt texts. I’ve googled this but nothing found…