This clever photo shoot delivers a hidden message about adopting pets.

Homeless animals are a major problem all over the world.

In the U.S., our shelters are jam-packed with millions of cats, dogs, and other furry friends in desperate need of a home. Sadly, far too many of them never find one.

But in recent years, a powerful slogan has caught on in a major way: "Adopt, don't shop."

Campaigns from places like PETA and the ASPCA encourage families to take home needy animals from shelters instead of buying designer pets from breeders. At least one recent survey shows that it might be working; the majority of Americans considering adding a pet to the family would reportedly be more likely to adopt from a shelter.

It's progress, at least.

Now the idea of adoption as a way to fight animal homelessness is making its way to other parts of the world.

India, for example — home to a mind-boggling 30 million or so stray dogs — is in desperate need of a way to shift the way people think about homeless animals.

That's why one organization staged a brilliant and emotional photo shoot to combat the problem.

The photos, shot by World for All, show happy families — two parents with a new baby, a young couple in love, a pair of giggling kids.

But there's something missing in each photo. Can you spot it?

Let's zoom out for a better view.

Cool, huh?

The eye-catching ads were created to promote a giant Adoptathon in Mumbai and brought in a ton of extra foot traffic. According to PetaPixel, the Adoptathon was a big success, with over 40 homeless animals finding new homes in just one day.

Not to mention, the images were a big hit in the photography/design community and with internet users all over the world.

The message? Pets aren't accessories. They're members of our families.

They need food and shelter. They need affection. But most of all, they need your love.

If you've decided that something's "missing" from your own family and that a four-legged friend might just fill the void, just know there are millions of them out there with plenty of love to give right back.

All they need is a chance.

*Campaign by McCann Worldgroup, Mumbai, Prasoon Joshi, executive chairman and regional ED AP, Pradyumna Chauhan, national creative director, Sharmad Khambekar, creative director, Pranav Bhide, art director, Pranav Bhide, copywriter, Archit Gadiyar, copywriter, and Amol Jadhav, photographer.