How is it possible to offer suggestions, which could lead to a resolution of the problem when you have already uninstalled avast.
1. You can't apply any suggestions we offer to avast.
2. You cant give us any information about the settings that you had within avast.
3. You can't or didn't tell us what the split of CPU usage, photo software/avast making up the 100%.
4. You used avast for a year with no problems, what changed, your settings, the photo program, xp sp2, what?
I think you have thrown the baby out with the bath water, AVG is lighter (but only slightly, no appreciable change on my system having dumped AVG), because I believe it does much less, the default setting scan very little.
Without avast on your system it is impossible to help resolve an issue supposedly involving avast!