Ok, I solved problem with updateThumbPreview... in last build it was used as php function not as js function. Also if I make suggestion I think it's worth to change printEditCommentLink with different if statement: if (zp_loggedin(COMMENT_RIGHTS)) {. Without that any administrator user without any privileges can edit any comment.
About cache you have right, I agree with you that in most scenario this is not worth to secure it. But if zenphoto gives me ability to disable hotlink to full image I also want disable access to picture in 640x480 size. This size is enough good to use on the another website in internet.
But overall I am very happy with that what I have now. So thank you for your help, advice and comments. I love Zenphoto as user who first saw php and linux environment