I'm missing the suport of WP_CONTENT_DIR and/or WP_CONTEN_URL.
my setup of wordpress is that its located in /usr/share/wordpress, that's also my DocumentRoot in apache.
but, all the content is located in /srv/www/wp-content/<domain>/. therefore I've
Alias /wp-content /srv/www/wp-content/<domain> in apache. and somewehere else
define('WP_CONTENT_DIR', '/srv/www/wp-content/<domain>');. it's working fine with wordpress' own media library.
Eazyest Gallery is showing me more or less the correct gallery folder as
../../../srv/www/wp-content/<domain>/gallery/. uploading some pictures into the gallery is successful.
but the main problem is that (not only) thumbnails are linked as http://<domain>/srv/www/wp-content/<domain>/gallery/<folder>/_cache/<picture>-150x150.jpg
seems to me that WP_CONTENT_DIR is not honored in any case.
what I would have awaited is that the gallery folder in the settings is just "gallery" and with the help of WP_CONTENT_DIR you get the path in the filesystem where the gallery is located. you can also use WP_CONTENT_URL for generating the correct url (btw, I have set this also in my config).
do you see any chance to get this into your plugin.