How to get first heading in Tumblr theme HTML without using Javascript?

Question

When we post a photo on Tumblr (or a video), it doesn't provide any option to add post title. This can be problematic from SEO point of view. So, is there any way I can get the text of first H1 tag of my blog post without using Javascript?

Currently, I am using just the description of the post but it takes all the text including the first H1 that is not required for SEO.

<title>{block:TagPage}&lsquo;{Tag}&rsquo; Search Results |{/block:TagPage}{block:PostSummary} {PostSummary} |{/block:PostSummary} {Title} - Space Pictures, Videos and News</title>

Example post: http://beautyaboveus.com/post/162118143903/northern-summer-on-titan