Theres a lot of old, deprecated and now wrong installation guides for the SilverStripe Image Gallery Module on the web that will lead you to where you dont want to. Dont trust them!
So a working installation of the image-gallery for git-people is to:
install silverstripe 2.4.* (latest)
get the modules via git:
cd mysproject git clone https://github.com/unclecheese/ImageGallery.git image_gallery git clone https://github.com/unclecheese/Uploadify.git uploadify git clone https://github.com/unclecheese/DataObjectManager.git dataobject_manager
login as admin