Validation error: "The itemprop attribute was specified, but the element is not a property of any item"
You should explicitly provide a type these properties (name, description, image) belong to.
In Schema.org, everything is a Thing. Thing has many child types, listed under "More specific Types". Start there and choose the most specific type for your content.
For example: WebPage, Article or maybe BlogPosting.
It could look like (using WebPage as example here):
<html itemscope itemtype="http://schema.org/WebPage">
If you use itemprop meta tag in header for your site title, description and so on.
only just add itemscope itemtype="http://schema.org/WebPage" in your html tag.
finally:
<html itemscope itemtype="http://schema.org/WebPage">