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100% WORKING METHOD ON HOW TO DISPLAY GRAPHIC WATERMARK OVER THE IMAGE:
MODIFY \includes\classes\oscThumb.php line 232 like this:
$params .= "&fltr[]=wmi|/phpThumb/watermarks/".WATERMARK_IMAGE."|".WATERMARK_IMAGE_POSITION."|".WATERMARK_IMAGE_OPACITY."|".WATERMARK_IMAGE_MARGIN;
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