I have the same problem. It appears to me that displaying blobs in a web-browser simply doesn't work the way it is described at php.net.
I have found a workaround where I write blobs into the filesystem and get them from there:
$getImg=ifx_query("SELECT LOTOFILE (thumbnail, '/daten/ifx/apache/htdocs/archiv/tmp/gfxPrint/tmpthumb/$getGfxPrintRow[assetid].jpg!', 'server') FROM koch_graphicsprint WHERE assetid = '$getGfxPrintRow[assetid]'",$connection);
echo "<IMG SRC=/tmp/gfxPrint/tmpthumb/".$getGfxPrintRow[assetid].".jpg></TD>";
I know this is not nice.
If you found another solution in between, please let me know!
yours,
Herwig