Given that Twitter has announced a feature that will allow users to attach photos directly to their tweets without having to use a third-party service, photo-sharing on the social network is never likely to be the same again. With that in mind, social media analytics company Sysomos decided to take a look at how people shared their photos on the social network before Twitter made its blockbuster announcement this week.

Sysomos took a snapshot of all photo-sharing activity on Twitter on May 30 to determine this data, but it says that photo-sharing activity on other days was similar. The company says that, on May 30, 14.9 percent of all tweets contained a link, and that 1.25 percent of all tweets contained a link to a photo — that means around 1/12 links shared on Twitter are photos. Given that Twitter users post around 170 million tweets per day, they are sharing 2.125 million photos on the social network in each 24-hour period.

Among the tweets that contained images, the most popular service to share photos with was TwitPic (45.7 percent). Yfrog was runner-up with 29.3 percent, followed by Lockerz (17.4 percent), Instagram (5.2 percent) and Flickr (2.1 percent).

Those percentages are likely to change very soon as Twitter rolls out its photo-sharing feature. In addition to allowing users to embed photos directly into tweets from Twitter.com and its mobile apps, Twitter is working on a way to allow people who do not own smartphones to tweet photos via MMS. Twitter’s market share of the photo-sharing space could be further increased, should a rumor that Apple will integrate Twitter’s photo-sharing feature into its iOS 5 firmware prove to be true.

For the most part, I am using Yfrog to share photos on Twitter. I used TwitPic in the past, but switched after the recent controversy surrounding the company’s terms of service. I occasionally use Instagram too, but I will certainly be checking out Twitter’s photo-sharing feature, which is being rolled out to all users over the next few weeks.

Which third-party service do you use to share photos on Twitter?