Symptoms
The following error report is generated on attempt to print any order/invoice in Magento backend:
ImageType is not JPG
a:5:{i:0;s:20:"ImageType is not JPG";i:1;s:"#0 lib/Zend/Pdf/Resource/ImageFactory.php(62): Zend_Pdf_Resource_Image_Jpeg->__construct('')
Cause
The error is generated by GD library (GD image processing module) due to unsupported image format used in the logo.
Solution
The solution is to change the uploaded logo for PDF print-outs to JPEG format at System > Configuration > Sales > Sales > Invoice and Packing Slip Design in Logo for PDF Print-outs section:
