See the world's toughest borders

An iconic image from the 2015 refugee move: crossing into the EU on the railway tracks between Serbia and Hungary to Europe. This crossing point closed in September but Europe's porous borders will certainly yield new tracks to travel. People detected at Europe's borders already surpassed last year's by the end of August: 350,000; and that doesn't even count people who got in without detection.

The border between South and North Korea has been closed and heavily militarized for 62 years. This sign marks the "bridge of no return", seen here seen from the South Korean side. Since the late 1990s, approximately 28,000 North Koreans have fled to South Korea. More recently, both countries agreed to hold brief family reunions near the border.

Disparagingly labelled the "tortilla wall" by Americans, walls and fences secure 1126 kilometers--a third of the actual border. With 18,500 officers are positioned along it, the border is one of the most-policed on the planet. Though many millions of Mexican citizens still travel to the United States to work and live as undocumented immigrants, a number estimated at 6.7 million in 2012.

It's a border that causes endless political trouble and deep tensions. Beautiful moments of life happen right at the border, but this peaceful scene on the Mexican side of the border is deceiving: 700 people are forcibly deported back to Mexico each day. For those who spent years in the States, many have a hard time adjusting to their new home.

Economic worlds clash in the Spanish enclaves Melilla and Ceuta, bordering on Morocco. Seeking a future in rich Europe, refugees from all over Africa seek a way to request asylum in a European country. In search of a better future, many try to climb the fences. With an extensive series of fences and Morocco taking more of an active role, fewer scenes like this are taking place.

According to satellite images, the frontier of Brazil's deforestation is defined by the border to Bolivia. Legal and illegal deforestation made Brazil's Amazon forest cover decrease by 20 percent during the last half century. However, Bolivia is also considered a deforestation hotspot that scientist say needs more study.

Though both countries share one island, they couldn't hardly be more different: The Dominican Republic is a tourist paradise while Haiti is one of the poorest countries in the world. Striving for a better future, many people move to the DR. In 2015 the country strengthened immigration laws to encourage migrants to leave and around 40,000 Haitians have now returned to their country.

Desert on the one and dense population on the other, the border between Egypt and Israel divides a Muslim-majority from a Jewish-majority. A peace that has held for more than 30 years has been marred in recent years by violent border incidents, increased militarization and tense political exchanges. Israel finished building a fence on the border at the end of 2013.

In some parts of the world, borders are not marked with patrols, fences and walls. This spot, marked by a three-sided stone, marks the borders of three countries: Germany, Austria and the Czech Republic. Part of the Schengen zone, free travel across these borders has only recently been limited due to the European refugee crisis.

Since the first Indian-Pakistani war from 1947 to 1949, the Kashmir region has been divided by the "Line of Control" between a Pakistan-governed, Muslim majority and an Indian-governed, Buddhist and Hindu majority. The line hasn't stopped terrorist attacks meant to establish an Islamic Kashmir that killed an estimated 43,000 people since 1993.

Until 1976 Western Sahara was a Spanish colony. To stake a claim, the Moroccan king settled 350,000 people in Western Sahara. The local Saharawis started an independence movement called Polisario Front. The war split Western Sahara, with the Sahrawi Arab Democratic Republic on one side and Moroccan held territory on the other. Down the middle runs a heavily militarized berm built into the sand.

Since 2002 controversial walls and fences were built that amounted to barriers stretching to more than 759 kilometers. In densely populated areas like this photo from Jerusalem, a high concrete wall nine meters high fortifies the border between Israel and the West Bank. In 2004, the International Court ruled that building a wall onto Palestinian areas is not compatible with international law.