Here is a great article covering this topic - Put some Life : How to add pictures on a folder in Tableau Server 

I hope this helps

Patrick

Please mark this reply correct if it resolved the question so others may easily locate the same response.

My problem is the same except I could find the folder on server.  When I placed my images there and used the html in the project description as per the article (which is where I started) I get a broken image thumbnail like the original poster.

Is there a permissions/enabling thing in server that will make this work?

See my answer below for your inquiry

Hi Clariberth

Actually i figure out how can i show the image on project folder and it working fine

First you need to show hidden folders then follow below path

      C:\ProgramData\Tableau\Tableau Server\data\tabsvc\httpd\htdocs

Place your Image there

Then on Project folder write this

!http://Server_IP:Port/Image.jpg!