Help with nokogiri

I’m trying to work with nokogiri but I have some problems
I need to iterate a string that has several tags with a base64
image
and change it for a url

example:

test</ p><img
src=“data:image/png;base64,iVBORw0KGgoAAAANSUhEUgA…”
alt = \ “”> bla bla bla <img
src=“data:image/png;base64,iVBORw0KGgoAAAANSUhEUgA…” alt = \ “”>”

Change to:

test</ p><img src=“http:www.blablabla.com” alt = \ “”> bla bla bla
<img src=“http:www.blablabla.com” alt = \ “”>”

How can I select these img tags, change the src content and return the
same
string modified ?

Thanks.

Well, I managed to this:

doc = Nokogiri::HTML::DocumentFragment.parse(string)
doc.css('img').map { |i| i.set_attribute(:src, 

http://www.blabla.com”)
}
p doc.to_s