As a workaround until I've found out if there is a basic/simple way to do this I have placed a hidden button on the row which sets a variable or the PK. And I'm hiding the image if the variable does not match the PK. It's working but still wondering if I'm missing a one step command.
In the portal table, create an unstored calc field, say, cGetRecNum, with the expression
Get ( RecordNumber )
Create a script with just Refresh Window (try Refresh Object or Refresh Portal, if your FM version has these commands).
Add an OnObjectEnter script trigger to the portal and attach the Refresh script.
The Hide if calculation is
PortalTable::cGetRecNum ≠ Get ( ActivePortalRowNumber )
Thanks for that. That's another variation of what I've done using the Variable. I just thought with all the newer features in FM 14 there may have been a one line command.