libguestfs tools howto guide for managing virtual machine images.

libguestfs-tools aka guestfs tools has a lot of tools that make this very easy for you.  You can easily mount partitons from an image with some of the commands below.

To mount a partition
#mount the kvmuser102821.img image and the /dev/sda1 partition from it to the local directory "mount"
guestmount -a kvmuser102821.img -m /dev/sda1 mount
 

To list partition info on the image:
virt-df image.img

Filesystem                           1K-blocks       Used  Available  Use%
kvmuser102821.img:/dev/sda1           20641404     768404   18824476    4%

 

To resize (expand) an image:

#first create the destination disk of the size you want:
qemu-img create -f qcow2 kvmuser102821.img-60G 60G
Formatting 'kvmuser102821.img-60G', fmt=qcow2 size=64424509440 encryption=off cluster_size=65536

virt-resize --resize /dev/sda1=60G kvmuser102821.img kvmuser102821.img-60G

Examining kvmuser102821.img ...
 100% ⟦▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓⟧ --:--
virt-resize: error: There is a deficit of 2260992 bytes (2.2M).  You
need to make the target disk larger by at least this amount or adjust
your resizing requests.

If reporting bugs, run virt-resize with the '-d' option and include the
complete output.

#try again by increasing the target slightly in this case to 60.1G
qemu-img create -f qcow2 kvmuser102821.img-60G 60.1G
Formatting 'kvmuser102821.img-60G', fmt=qcow2 size=64531883622 encryption=off cluster_size=65536
 virt-resize --resize /dev/sda1=60G kvmuser102821.img kvmuser102821.img-60G
Examining kvmuser102821.img ...

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