How do you detect if 'update' save fails?

So I’m updating multiple model objects in one go with something like
this in my controller:
=> Photo.update(params[:photo].keys, params[:photo].values)

When the update fails due to validation errors, how do I detect it?
The Rails API says:
“If the save fails under validations, the unsaved object is still
returned.”
So I can’t simply do this:
=> if Photo.update(params[:photo].keys, params[:photo].values)

Any suggestions?

photo=Photo.find params[:id]
unless photo.update_attributes params
#error handling
end