Hello,
as far as I know, using the dashboard, there's no way to either create an image or load, in the catalogue, an image you created.
For creating an image, you need to use kvm (see a description here http://forums.openstack.org/viewtopic.php?f=15&t=523&p=1716&hilit=red+hat#p1716 (http://forums.openstack.org/viewtopic...) ) or some tools specifically designed to do that (see http://docs.openstack.org/essex/openstack-compute/admin/content/creating-new-images.html (http://docs.openstack.org/essex/opens...) ).
This means that starting from an installation ISO image, you create a boot-able "disk" or (better) a boot-able image.
Once you have created an image, you have to load it into the catalogue by calling glance's CLI. See here for details: http://docs.openstack.org/essex/openstack-compute/install/yum/content/uploading-to-glance.html (http://docs.openstack.org/essex/opens...)
This second step actually reads the image (the file) and loads it into glance.
Alternatively you can download some per-fabricated image from a "free" catalogue you find in Internet (see, for example here http://www.turnkeylinux.org/ (http://www.turnkeylinux.org/?) ) and load such an image into glance (with the steps described in the previous step).