Right, this is a config hosting problem. After treatment photo are owned by Web server user. So if isn't the same as your FTP user you can't delete it. Contact your hosting admin to correct Web server conf.
Since 1.0.6, eXtGallery have an extended upload option that require Java plugin and allow you to put batch photo in on click from user website side. The 1.0.7 version that is in devellopement allow to bypass php max_upload_size with this extended upload feature :
make long traitment (photo resizing for exemple) in PHP is very difficult. So the way i choose is to make a Java applet to allow admin an user to make large upload at once. I just starting this project.