Twitter has updated their 140-character policy which no longer factor certain add-ons including pictures into a message’s length.
From a quote from @Twitter
Say more about what’s happening! Rolling out now: photos, videos, GIFs, polls, and Quote Tweets no longer count toward your 140 characters.
This seems to mean the new policy exempts media attachments such as photos, videos and polls from the character limit, as well as tweets that are quoted in a retweet.
You can check the tweet out yourself here.