[Zope] html2pdf

Hi, I've a big problem with html2pdf. I've a zpt with an image "myimage.jpg". The content of "myimage.jpg" changes every time. When i call the script html2pdf on the page the pdf is generated correctly but....if i recall subsequently the page I have always the first "myimage.jpg". It seems the image "myimage.jpg" is cached (i don't know where! I haven't set anything about cache). how can I resolve this problem? Thanks a lot!! Massimiliano