I found out that image tag and iframe tag are followed and indexed by search engines so it is harming my seo even though I have all my hyperlinks nofollow, how to add nofollow to img and iframe tags.
Thanks
To stop crawlers (robots) from crawling and indexing iframe & img tags you can use robots.txt or meta tag!
rel="nofollow" attribute is used in links (hyperlink) related with <a> tag which may decrease your PageRank, this is a common practice used to fight link spamming.
Robots <META> tag
<META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">
You can also use more aggressive approach!
robots.txt disallow
Disallow: URL or a subdirectory goes here
rel="nofollow" is only affective for anchor links <a href it won't do much for iframe or image. If you are so concerned about it then simply don't use them!