Actually there are many. It definitely not another service like tweetlonger or similar.
All you need is an image editing software which can write text on images. For best experience, start with a blank template, and just write some text on it using your favourite image editing tool. On windows, even MS Paint will do. I've found one for my android device.
Quoting this tweet as reference.
A pic is worth more than "140" words...Edited with #Phonto. @phontograph http://t.co/kQselzloYo pic.twitter.com/KuLCPfVywY
— Arun Jayapal (@deostroll) June 2, 2014
Happy browsing, tweeting...Although you can post more than 140 characters in an image, you still are limited to an upper bound. I don't know what that is, but hopefully someone will discover that one day. As for an experience POV, people who are used to 140 characters might welcome this. However, if you hated twitter in the first place, I guess you can hate it a little relatively lesser now. I am not telling those folks to like the service, at least, like the fact, that I am writing this blog to let you know of such hidden features!
Meanwhile, here is an infographic which talks about sizes and dimensions for images that can be used on twitter:
( Source: http://freshtakeoncontent.com/twitter-image-sizes-dimensions/ )