OK. What I'd recommend is uninstalling the printer and NOT using HP's software. How you uninstall it is:
1. System Preferences, Print & Fax, locate the printer on the left side then highlight it and click the - at the bottom of the preference.
2. Re-start the computer.
3. Re-open the Print & Fax preference and this time click the + symbol on the left. You iMac should locate the machine, simply add it following any instructions.
4. After it is installed use Image Capture to scan. You can launch IC various ways the easiest I've found is locate the app in your Applications folder and drag it to your Dock. Another simple way is to use Spotlight which you can shortcut by clicking Command, Spacebar then type Image Capture.
That should take care of it.
Regards,
Roger