Update: Sept.. 12
The government can look at emails without a warrant if they are more than 180 days old (source). There are calls in Congress to tighten the requirement for a warrant. But, right now, theoretically, the police could scan cloud backups for c.p. images (by hashmark) that had been stored for more than 180 days, without a warrant. I haven't heard of this actually being done.
Update: Oct. 4
Deleting an image from a computer often results in the Cloud Service deleting it from a backup. But police could still try to look for older deleted images in a cloud, just as they can on a hard drive. But I haven't heard that this has actually happened.