American bills have portraits of the country's Founding Fathers and former presidents. Chinese notes have Mao Zedong and Indian ones have Mahatma Gandhi, but none of them feature any women. Many other currencies also stick to men, sometimes including a token woman or two.

Now there are calls for the US to put a female on the $20 bill. "The United States needs to show the world that we, too, recognize and value the contributions of women," says Susan Ades Stone, executive director of the campaign group Women On 20s.

"Our money says something about us and what we represent as a society. So if we're all about gender equality and diversity and inclusion, let's walk the walk."

The US currently has seven bills in circulation, all of which feature distinguished, deceased American statesmen.

Women On 20s conducted an online poll and asked people to choose which of 15 historical female leaders they would most like to see on the note.

The candidates included civil rights activist Rosa Parks, birth control pioneer Margaret Sanger, suffragette Susan B Anthony and Harriet Tubman who escaped slavery and went on to lead other slaves to freedom.

More than 200,000 people voted in the first round, and the second round - set to last a few weeks - is currently underway.

Once the final poll closes, the group will petition President Obama to replace Andrew Jackson with the chosen woman.

Many wonder why Jackson - the seventh president of the US - hasn't been removed from the $20 bill already. He is especially unpopular with Native Americans due to his signing and enforcing the Indian Removal Act of 1830, which forced tribes off their land. Thousands of Native Americans died on the journey west - known as the Trail of Tears - from exposure, starvation and disease.

His controversial legacy is one of the reasons why Women On 20s chose to target this particular bill for change.

Meanwhile in Canada, more than 54,000 people have signed a petition to put a woman on a banknote there after the sole female to appear on the country's currency, Therese Casgrain, was replaced in 2011 by an icebreaker ship.

"When we open our wallets and see the faces of four male prime ministers and Queen Elizabeth, the subtle message is that Canadian women aren't worthy of being celebrated," says author and historian Merna Forster who started the Canadian campaign.

"Sexist banknotes are unacceptable in a country that boasts of being a world leader in promoting gender equality… If women are equal to men in Canada, they should be equally represented on our banknotes."

A similar petition was launched in the UK in 2013 after it was announced that Winston Churchill would replace Elizabeth Fry - a social reformer and philanthropist - on the £5 note. More than 36,000 people signed it and convinced the Bank of England to put the author Jane Austen on the £10 note from 2017.

In both the UK and Canada, the Queen's portrait is on many banknotes. But, critics say this doesn't count because she appears as a monarch rather than for her achievements. Plus, she will eventually be replaced by a male heir.

Although the UK petition was a success, campaigners in all three countries - the US, Canada and the UK - have called for only one woman on a note. But is that enough? Should half of all portraits on currencies be of women, better reflecting the makeup of the population?

That's what's happened in Sweden. "We thought it was very important to feature an equal number of men and women," says Susanne Eberstein, the chairman of the General Council at the country's Riksbank. "It was well in line with our aims. It was very natural."

Women appear on three of the banknotes there, although one of those depicted is Mother Sweden. A new line of Swedish notes, to be introduced in 2015 and 2016, will feature three men and three women - actress Greta Garbo, Pippi Longstocking author Astrid Lindgren, and opera singer Birgit Nilsson.

(BBC)