[TYPO3-content-rendering] [TYPO3 6.0.6] TypoScript for own content element

[Simon]

I defined a new content element type named "imgTest" via extTables.php.

For the frontend rendering I am using the following TypoScript.

tt_content.imgTest = COA 
tt_content.imgTest {
  wrap = <div class="imgTest">|</div>
 
  #output a image that was added to the content element
  5 < tt_content.image.20

  10 = TEXT
  10.field = header
  10.wrap = <h2>|</h2>

}

Everything is rendered as expected except this does not display the image I added to a test content element.
I also tried to get the image with IMAGE and IMG_RESOURCE, which I would prefer, but also no success getting the image from the content element.

Any suggestions?