First, on the server, edit zope.conf to add the lines for WebDAV support. It's in the /instance/etc directory.

<webdav-source-server>
   # valid keys are "address" and "force-connection-close"
    address 1980
    force-connection-close off
</webdav-source-server>

Restart Zope.

If you're using the Mac, open a terminal and type this in, to prevent creation of those pesky .ds files. (note... this hasn't worked for me)

defaults write com.apple.desktopservices DSDontWriteNetworkStores true

http://plone.org/documentation/faq/mac-os-x-ds-store-files-webdav

Now, on the Mac, type command-k, then put in the url of your site. It's best if you put the URL right to the folder you want to put the pictures in.

Instructions here.

A helper script that adds titles to uploaded photos, based on their file name.

You probably don't want people gaining WebDAV access to your entire site. From the ZMI, turn off WebDAV access at the root folder from the Security tab. Then go to the folders where you want it and grant the appropriate permissions.

Preparing pictures for upload

Pictures exported from iPhoto, sized 600px wide are about 100K in size. If you run them through graphicConverter you can quickly shrink them to 20K with no visible quality hit.