The Baltimore Grotto (a chapter of the National Speleological Society) presents its motto: “Take nothing but pictures. Leave nothing but footprints. Kill nothing but time.” These three short sentences express a philosophy of respect and appreciation for nature that allows human beings to enjoy the natural world without ruining it.

“Take nothing but pictures” encourages explorers of nature to leave it as they found it without removing anything. It is tempting to claim a souvenir or start a collection of natural objects, but this part of the motto reminds us that nature should be left for others to enjoy. We can take pictures to preserve memories and scenes, but that is all we should take.

“Leave nothing but footprints” reminds people not to litter or deface the natural world. It's so easy to drop a piece of trash and not bother to pick it up or to draw some graffiti on a rock to preserve our name, but this actually diminishes the experience of nature for the next person. There is no reason to leave anything behind us in the natural world except perhaps our footprints, which will fade quickly. We should not seek to impose ourselves on nature, carelessly or deliberately.

“Kill nothing but time” also cautions people to leave nature alone. Animals should be observed in their natural habitats rather than killed for sport, according to this part of the motto. It is good to spend time in nature, not doing anything but looking and enjoying, even if this is considered merely “killing time” by many.

The above motto, used by members of a cave exploration society called the Baltimore Grotto, expresses a feeling of great reverence for the natural world. In an age where so many people exploit the environment for personal gain, the motto invites us to rethink our relationship with nature by seeing it as something to be nurtured, cherished, and cared for.

All too often, humans take from the environment. They take things that they regard as being valuable, such as gold, copper, and timber. In taking from the environment like this, humans upset the delicate balance of the ecosystem and spoil it for future generations.

Humans also leave many things behind in their exploitation of the environment, such as the tons of garbage left floating in the world's oceans. All across the world, aquatic life and the environment it inhabits are under threat from humans leaving behind things in the oceans and seas—such as items of plastic—that they no longer need or want, and which don't belong there.

Finally, one quick glance at the world shows humans killing numerous species, reducing them to the brink of extinction in the process. The wholesale destruction of natural habitats, such as the Amazon rainforest, also involves the killing of animals, who depend upon rainforests for their survival.

While the Baltimore Grotto, an organization founded in 1952 and dedicated to “the exploration, study and conservation of caves,” does use the phrase “take nothing but pictures, leave nothing but footprints, kill nothing but time” as its motto, the origins of the phrase, which varies in usage, are unknown. That said, the idea behind the phrase, is deeply rooted in ecological conservation and simply refers to the need to minimize one’s impact on nature, including refraining from removing plants, rocks, or other natural things from protected areas.

Humanity’s interaction with the Earth’s natural environment has been very destructive at the individual, corporate, and national levels. Industrial pollution is well-documented, as is the destruction to the natural environment carried out by many governments around the world seeking to exploit natural resources. Less appreciated is the destructive impact of individuals and small groups on the environment. The phrase “take only pictures, leave only footprints, kill nothing but time” is intended to address this "micro" level of humanity by impressing upon tourists, hunters, and others the need to respect nature and to minimize the adverse impact upon nature caused by tourists, hunters, hikers, and others. “Leave nothing but footprints” means clean up your waste from the lunch or snacks your brought along on your adventure. “Kill nothing but time” means refrain from killing wild animals and plants whose natural habitat you are currently invading.

"Take nothing but pictures.
Leave nothing but footprints.
Kill nothing but time." 
      

This quote was the motto of the Baltimore Grotto, a caving society and it is part of the "Leave No Trace" philosophy of naturalist all over the world.   It basically means that when we are in a natural setting we should leave no trace of human intervention.  We should, by all means, take pictures for our memories of our adventures.  We should not leave anything behind such as trash, beer cans, paper, tobacco filters, plastic bags etc.  We should be careful not to kill any of the wildlife in the area which includes animals, plants, and any living thing. We are stewards of this beautiful planet and we should not leave our imprint on any natural area. The motto itself could have come from the quotation,

"Take only memories, leave only footprints," by Chief Seattle