If you're storing images - you probably want to use a file system. They are much better than databases at storing files (also, running a lightweight web server makes it really quick and low overhead to serve them out).
if you need to split and replicate the data, you can do so pretty easily (rsync works really well, and with some good structuring of directories and maybe some small shell scripts you can make all this happen *really* fast).
You may want to index them in a database though. Note that this is what every photo app does (iPhoto, Gallery and f-spot at least).
MySQL is not geared towards shared storage clustering. You can use MyISAM tables with external locking - athough when one machine goes down, you may have to run a myisamcheck on the table.
If you are intent on storage the images inside the database, it's probably best to partition the data set and use replication.
However, this isn't really the right forum for non NDB related questions.
Stewart Smith, Software Engineer - MySQL Cluster
MySQL AB, www.mysql.com
Jumpstart your cluster:
http://www.mysql.com/consulting/packaged/cluster.html