That is indeed a nice question and I would love to answer it in detail:
What is Keyword Density?
Keyword density means the ratio of your focus keyword compared to other related keywords. In short how repeatedly are you using different variations of the Major keyword.
Publishers believe that the good ratio of keyword density is 1.5%-3% but I never believe on such mathematics but common sense! As long as you are good at writing english you will never use repetitions in your articles instead you would prefer using synonyms (LSI keywords) and that is what you must do while publishing articles to stay on safe side.
Rule of Thumb: Use Related Keywords in Opening Para and write a para of no less than 150 words. Adopt a natural tone, don’t forcibly add related keywords everywhere. Using a keyword once nicely is better then stuffing it several times in Content.
Is Image equal to 100 words?
It is merely a proverb my dear and not reality. It means that a picture can give a much better understanding of things than simple plain text. Same applies to Videos when compared to Plain images. You image does surely not count when we talk of Keyword density.
What Are LSI Keywords?
Latent semantic indexing keywords (or LSI keywords) are nothing but SEO terms for related keywords or synonyms. Before this term has came into picture the only thing to determine relevancy of article was keyword density. Which means if your post is about “Mobile Phones” and you have used it 5 times throughout the article than your competitor needs to use it 6 times to beat your position in Google search, but let me ask you, is it fair?? Same Thing applies for search engine, instead of taking high keyword density into consideration, search engine bot now a days look for related keywords (Latent semantic indexing keywords) throughout the article. It doesn’t mean that we shouldn’t maintain keyword density for target keyword in our article, but over optimization can cause issues. That is why I mentioned to keep it between 1.5- 3 %.
What is safe keyword density for blogs?
Never believe on maths when it comes to Content, always value your common sense. Anything that is overused irritates the readers as much as it does Search robots. So as long as you keep a natural tone and use keywords when required and not forcibly, you are on a safe side. Use related or LSI keywords in your opening paragraph and also your headlines i.e.
<h2> or <h3> tags
Let me know if you need more help dear brother