I use an Image Control and as an expression
$P{cMandLogo} != null ? net.sf.jasperreports.engine.util.JRImageLoader.loadImage((byte)$P{cMandLogo}) : null
cMandLogo is passed to the report engine as Parameter, which is nothing more as the content of a database field. Instead of $P{param} you should be able to use $F{Field}.