Ho considerato il tuo consiglio, sono andato a trovare la guida e in riferimento appunto a "addimage" č necessaria la libreria GD. Onde evitare problemi il punto 2 parla di addJpegFromFile, potrei provare a cambiare metodo?

addImage(img,x,y,w,[h],[quality=75])

Add an image to the document, this feature needs some development. But as it stands, img must be a handle to a GD graphics object, and one or both of w or h must be specified, if only one of them is specified, then the other is calculated by keeping the ratio of the height and width of the image constant.
The image will be placed with its lower left corner at (x,y), and w and h refer to page units, not pixels.

2<addJpegFromFile>

addJpegFromFile(imgFileName,x,y,w,[h])

Add a JPEG image to the document, this function does not require the GD functionality, so should be usable to more people, interestingly it also seems to be more reliable and better quality. The syntax of the command is similar to the above 'addImage' function, though 'img' is a string containing the file name of the jpeg image.