Currently there isn't a way to determine if an image in the Image Editor has any changes.
There is a HistoryOnCurrentImageChanged() event which goes some way to providing the functionality, but this doesn't fire until a tool is committed.
For example, if you load an image, and select the Hue tool, and then drag the hue slider and change the image, this won't trigger the HistoryOnCurrentImageChanged() event until the user commits the tool e.g. clicks another tool or clicks off the image...
What would be perfect would be to have a HasChanges() property on the image editor that gets set to true when any aspect of the image is edited e.g. a tool slider is moved and the changes are not yet committed.
This would allow things like being able to have the the Save button disabled until the image is edited. Or being able to warn a user they are about to lose their changes if they have edited (say) the hue but have not yet committed the tool.