First lets remark that a portrait photo is not the same thing as your main user avatar, the last one being the thumbnail that is displayed both in your dashboard and the icon displayed when you are a follower (that also applies to your main tumblr blog).

Bear in Mind that each tumblr blog has its own Avatar/Portrait Photo

If you want to insert a profile picture within your description box on Tumblr, follow the tutorial below

How To Add an Avatar/Profile Picture To Your Tumblr Blog

1. Upload your Portrait Photo/Avatar to your particular Tumblr Blog on Blog Settings >> Portrait Photo option. (each blog has its own portrait photo/avatar)
2. Go to Customize Theme >> Edit HTML and paste the following code:




<div><a href="/"><img src="{PortraitURL-128}" /></a></div>




3. It’s not easy to tell you exactly where to paste the code, since each Tumblr Theme is different, but we suggest you look for the tag {description} and add the portrait photo code before or after it. Be careful, since this same tag could be surrounded by other p and div tags.
4. Update Preview >> Save >> Close

If you want to display a smaller Avatar on Tumblr

You have different sizes available, just replace the one above with one of the code snippets below:

{PortraitURL-16}
{PortraitURL-24}
{PortraitURL-30}
{PortraitURL-40}
{PortraitURL-48}
{PortraitURL-64}
{PortraitURL-96}