Please make sure your image is a RAW image before uploading.
While you can use QCOW2 images, they do not support copy-on-write operations. As a result, launching compute instances from these images or taking snapshots will take longer.
Ensure you have the qemu-utils package installed, as it provides the tools required to convert a disk image.
On Debian or Ubuntu:
sudo apt-get install qemu-utils
On Fedora or CentOS:
sudo yum install qemu-img
On a host with qemu-utils installed, convert the QCOW2 disk to a RAW disk:
qemu-img convert -O raw kvm-image.qcow2 raw-image.raw
On a host with qemu-utils installed, convert the VMDK disk to a RAW disk:
qemu-img convert -O raw vmware-image.vmdk raw-image.raw