I want you to look into the Thymeleaf’s documentation of Standard URL Syntax and specifically the context-relative and server-relative url patterns.
Context-relative URL:
If you want to link resources inside your webapp then you should use
context relative urls. These are URLs which are supposed to be
relative to the web application root once it is installed on the
server. For example, if we deploy a myapp.war file into a Tomcat
server, our application will probably be accessible as
http://localhost:8080/myapp, and myapp will be the context name.
As JB Nizet the following will work for you as I have used thymeleaf personally in a webapp project,
<img th:src="https://stackoverflow.com/questions/29460618/@{/images/test.png}"/>
and the test.png should be under your project root inside the webapp folder. Something navigated through roughly like,
Myapp->webapp->images->test.png
Eg:
<img th:src="https://stackoverflow.com/questions/29460618/@{/resources/images/Picture.png}" />
Output as:
<img src="https://stackoverflow.com/resources/image/Picture.png" />
When you hit http://localhost:8080/myapp/resources/images/Picture.png in you browser then you should be able to access the image for the above syntax to work. And your resources folder will probably under webapp folder of your application.
Server-relative URL:
Server-relative URLs are very similar to context-relative URLs, except
they do not assume you want your URL to be linking to a resource
inside your application’s context, and therefore allow you to link to
a different context in the same server
Syntax:
<img th:src="https://stackoverflow.com/questions/29460618/@{~/billing-app/images/Invoice.png}">
Output as:
<a href="https://stackoverflow.com/billing-app/showDetails.htm">
The above image will be loaded from an application different from your context and if an application named billing-app is present in your server.
Sourced from: Thymeleaf documentation