Image copyright @Broadstbullyt

Social media challenges have seen people dance, step over an invisible box and douse themselves in icy water.

But it's workers in the US service industry who have become the beneficiaries of the latest trend - the #TipTheBillChallenge.

As the hashtag suggests, the challenge consists of adding a 100% gratuity to a bar or restaurant bill.

Hundreds of people have shared images of the generous tips they have given or received, with many using the hashtag to highlight the poor wages of service staff in America.

One of the most widely-shared images is of a receipt dated 28 February 2018.

The image has resurfaced recently and inspired others to take up the philanthropic challenge.

Image copyright @mariahmargolis

Many of the photos have been shared by the happy recipients of the random acts of kindness, often accompanied by captions expressing glee and gratitude.

@Nessaaa_12 on Twitter shared a photograph of a $22.93 (£18.03) tip she received and thanked the generous stranger.

While @toriivoelker wrote that receiving a $65.23 (£51.30) tip "legit made my whole night".

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While most of the chatter around the hashtag is focused on the kindness of strangers, some have used it to highlight the working conditions for service industry workers.

Twitter user @Eugenius48, from Texas, USA, tweeted to urge servers and student members of the National Collegiate Athletic Association (NCAA) to "start a union".

Others wrote that "customers should #tipthebill AND make sure their servers aren't being exploited".

Another wrote: "As a server your only source of income are tips. If someone tips 50% or more that goes a long way. Mentally and financially."

Twitter user @PayPay_7 wrote: "Please tip your servers. Speaking as a server at two restaurants, I still make barely enough to make ends meet."

A 2017 YouGov poll found that 44% of Americans were in favour of scrapping the tipping system for higher wages. This was an increase from 36% in 2013.

It is not the first time that the politics of tipping has sparked debate on social media.

In 2017, a waitress was refused a tip because of her gay pride tattoo. While, a viral image of a racist note on a receipt was in fact "entirely fabricated".