In the OpenStack context, an image is a file that contains a virtual disk from which you can install an operating system on a VM. You create an instance in your OpenStack cloud by using one of the images available. The VMware Integrated OpenStack Image Service component natively supports images that are packaged in the ISO, OVA, and VMDK formats.
If you have existing images in vSphere that you want to use in OpenStack, you can export them in one of the supported formats and upload them to the Image Service. If you obtain an image that is in an unsupported format, you can convert it as part of the import process. Unsupported formats are RAW, QCOW2, VDI, and VHD.