I know, that's 2 Mb per photo. Is it possible to raise that maximum? (And how ...?) I got a lot of photo's that are 4 Mb in size and over.

I presume you are refering to the limits for the Zenphoto uploads. This is a php configuration setting (see note on the upload tab.) FTP of course does not have this limit.

BUT, a word of caution. Your server will have to have both the power and the memeory to resize these images down to the sizes used in the gallery. Most installations will not do so well with such large images.

Do you really need them on the server at that size? If not, resize them before presenting them to Zenphoto. If you do need them that big you will need a server that can support them. Among other things, you may need to be able to use the Imagick graphics library.

Yes, I am well aware of it. Most of my albums I'll scale well within the advised limits. But I have a number of albums in 300 dpi, and that is always big. The other thing is that the boss insists on it.

I had a bit of a problem convincing my boss.
My idea is to store as much as possible in Flickr. Use the Flickr plugin to show it in Zenphoto.

But I have a few albums (fortunately, not a lot) that have to be in 300dpi for clients to download.

If you need to raise the upload limit contact your host. For the web the dpi value is not of importance, it is the real pixel dimensions that is. Such 300dpi images are huge and might overload your server. http://www.zenphoto.org/news/troubleshooting-zenphoto#11