Prevent indexing images <img>

Hi

Have you encountered this problem, you know, when you have no choice but 
to use an img tag instead of a type block tag with a css 
background-image in an html page, and these images which used for style 
are found indexed?

I found myself many times in this situation during creation and 
integration of branding site, where the css background-image or 
javascript could not help me, and where i had to use an img tag... [see 
all my description here 
<https://www.w3.org/community/html5spec/2015/01/22/107/>]

These are the images that construct the graphic but in no way serve the 
SEO content and have no particular meaning with it. However, the image 
search pages on the search engines find themselves “polluted” by them, 
rather than proposing relevant content.

I wonder me if an attribute  noindex = “noindex” like robots meta tag 
could solve the problem. This could check the flow of indexed images.

< img src = “./images/character.jpg” noindex = “noindex” alt = “A 
character used for the style but uninteresting from an SEO point of view” />

What do you think about ?

Regards,

Aurelien