Brands continue to invest heavily in their presences on social media stalwarts like Facebook and Twitter and when it comes to newcomers, Pinterest seems to be creating the most buzz.

But the company that Facebook agreed to purchase for $1bn, Instagram, is quietly seeing adoption from a growing number of brands.

According to social analytics firm Simply Measured, 40% of the brands on the Interbrand 100 now have an account on the popular mobile photo sharing service.

Brand interest in Instagram isn’t exactly surprising despite the fact that Instagram is just photos. Earlier this year, Instagram had just 15m users; today it counts some 80m. And those users are posting a staggering number of photos — 4bn of them in total thus far.

The brands building the biggest audiences on Instagram are familiar faces. MTV, Starbucks and Burberry have more than 800,000, 750,000 and 450,000 followers, respectively. All told, eight of the top Interbrand 100 brands on Instagram now count over 100,000 followers. By category, the brands having the most success on Instagram are in the luxury category, and include names like Tiffany & Co., Audi, Hermes, Gucci and Mercedes-Benz.

What can brands expect from Instagram?

According to Simply Measured, Instagram can be a productive channel for brands — and it doesn’t have to be a tool to drive engagement on more robust social networks like Facebook and Twitter. It points to Audi as an example of this:

Audi is a prime example of a company that has taken Instagram seriously and seen it pay off. While they don’t have the audience of some other top Instagram players…they engage the audience they do have – which, at 104,511 and growing, is nothing to scoff at – much more effectively.

Since June 20th, Audi has 4.5 engagements per follower on Instagram. How does that look on a large scale? They average 1,423 “likes” and 34 comments per photo. Paired with a relatively high frequency of posts (normally one a day), this adds up quickly.

Of course, for many brands, whether “likes” and comments bolster more meaningful metrics (like sales) is still an unanswered question, but for those brands looking to build up a social media presence that appears to be engaging in some fashion, it appears that posting images to Instagram can be a worthwhile exercise.

Assuming that Facebook’s acquisition of Instagram is approved and the photo sharing service continues to grow like a weed, it won’t be surprising to see Instagram taking a more prominent role in discussions about next-generation social media sites worth investing in.