Can I use itemprop image directly?:<article itemscope itemtype=http://schema.org/Article><img  itemprop=image src=1.png><h1 itemprop=headline name >Title of the post</h1><div>2016-01-07</div>           <p itemprop=articleBody>This is the body of the post</p></article>Or should I embed inside ImageObject?<article itemscope itemtype=http://schema.org/Article><div itemprop=image itemscope itemtype=http://schema.org/ImageObject>    <img itemprop=contentUrl url src=1.png alt=alt of the image></div><h1 itemprop=headline name >Title of the post</h1><div>2016-01-07</div>           <p itemprop=articleBody>This is the body of the post</p></article>When I use the Google tool (www.google.com/webmasters/markup-helper/) it gives me the first option.But then the testing tool gives me an error:  The attribute image.itemtype has an invalid value
image property inside Article with or without ImageObject?
google;schema.org;microdata
From the perspective of Schema.org, both ways are fine, as the image property expects an ImageObject value (your second example) or a URL value (your first example).As always, a specific consumer might support only one of these two ways.For many of Googles rich results, an ImageObject is required, because Google wants to see more data about the image, which is not possible when providing just a URL. For example, their Articles rich result requires the height/width properties for the ImageObject value.