Clear Recent Pictures in MS Paint contains a registry file to delete the recent file list in Microsoft Paint as explained here.
This registry file deletes a registry key that contains the list of recently opened pictures in Microsoft Paint. The registry key will be restored after you reboot, leaving your recent file list empty. You can also edit the registry to delete what you want instead of everything.
Download 'Clear Recent Pictures in MS Paint' and extract Clear Recent Pictures in MS Paint.reg.
Double-click on Clear Recent Pictures in MS Paint.reg.
Click Yes when prompted by User Account Control. Click Yes when prompted by Registry Editor.