You could also use a $wikify widget, as explained in Wikification:

<$tiddler tiddler="Constant strings cannot be combined with transclusions">
  <$wikify name="myImageName" text="{{!!title}}.png">
    <$image source=<<myImageName>>/>
  </$wikify>
</$tiddler>

This works because TiddlyWiki acts like {{!!title}}.png is directly within the text of a tiddler when you use the $wikify widget, and as we'll see in another example further along in the section, putting a transclusion adjacent to constant text works fine in running text.

However, the $wikify widget unnecessarily complicates things here, and it tends to be slower than solutions that don't use it, so it's not normally a good solution for simple problems like this one.