Artists Justus Becker, aka COR (L) and "Bobby Borderline" work on their graffiti mural on a fence surrounding the construction site for the new head quarters of the European Central Bank (ECB) in Frankfurt, March 14, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 14, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Justus Becker, aka COR, works on a graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank in Frankfurt, March 12, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 12, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Justus Becker, aka COR, stands next to his sketch while working on his graffiti on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 13, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 13, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Justus Becker, aka COR, works on a graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 13, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 13, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Justus Becker, aka COR, poses for a photograph with a spray can while working on a graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 12, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 12, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Justus Becker, aka COR, works on a graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 14, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 14, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Justus Becker, aka COR, works on a graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 14, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 14, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Artists Justus Becker, aka COR (L ) and "Bobby Borderline" fist bump after finishing their graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 14, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 14, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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People look at artists Justus Becker, aka COR and "Bobby Borderline" working on their graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 14, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 14, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Artist Justus Becker, aka COR, carries his equipment as he arrives to paint a graffiti mural on a fence surrounding the construction site for the new headquarters of the European Central Bank (ECB) in Frankfurt, March 14, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 14, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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Artists Justus Becker, aka COR (L) and "Bobby Borderline" are seen in Becker's studio as they draw sketches for a graffiti mural in Frankfurt, March 15, 2014. The European Central Bank (ECB) has allowed graffiti artists to use the fence around the construction site of its new headquarters in Frankfurt am Main as a public gallery, where they can share their - often politically charged - art. Justus Becker, who helps curate paintings at the site, and a fellow artist who goes by the name "Bobby Borderline" recently completed a new work of street art on the fence. Picture taken March 15, 2014. REUTERS/Kai Pfaffenbach (GERMANY - Tags: BUSINESS SOCIETY)

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