That represents 4.8% of the estimated $55.2bn global art market, says the Hiscox Online Art Trade Report 2015, and by 2019 Hiscox expect the spend to rise to $6.3bn. Other key findings in the report show that:
• investment return is a growing motivation for online art buyers, with as many as 63% driven to purchase by a piece's potential return on investment;
• 84% of online transactions still take place below £10,000;
• online art market platforms mean having a physical gallery or auction house has become less important but is not redundant;
• social media affects art-buying decisions, with 24% of respondents saying posts by museums, galleries and artist studios had a direct influence on their art buying decisions.
Robert Read, head of fine art at Hiscox, said: "The rise in online art buying is even greater than we anticipated.
"The speed and confidence with which new and established collectors are adapting signals a new era as buying art becomes an omni-channel experience.
"Physical gallery space and auction houses can no longer act in isolation; online channels and social media have an important part to play and, when combined, prove to be attractive."
ArtTactic, the London firm specialising in art market research and analysis, conducted the survey in January and February 2015, securing responses from 519 international art buyers surveyed through their client mailing list, Twitter and Facebook and Own Art's mailing list.
Most respondents also took part last year, although ArtTactic extended the sample to focus on new buyers.
"This has allowed us to get a better idea of current online buying trends and behaviour among this next generation of buyers, and to better understand their concerns and future expectations when it comes to buying art online," said founder Anders Petterson.
"Although the central focus is around fine art, we have also explored online buyers' buying habits of other collectibles online." The report argues that art buying patterns and motives are changing.
"Almost half of this year's respondents (49%) said they had bought art online in the last 12 months, up from 38% last year. This indicates that further progress has been made towards mainstream adoption. Particularly popular among new collectors, the online art market continues to make collecting accessible and attainable to a broader demographic - good news for the whole industry."
Hiscox say that the majority of online art transactions still take place at a lower price point, with 41% of respondents saying their average price paid was less than £1000.
However, a growing number also cited investment return as a reason for buying.
Many of the reasons for buying online, such as convenience and a less intimidating experience, are fairly obvious, but less so is the ability to find new artists, cited by 71% as a key factor.
Mr Read expects activity to rationalise.
"There are too many players in the online art market, as one would expect at this stage of the development cycle, and it is still impossible to say who the winners will be," he said.
"We will have to wait for a couple more years of mergers, acquisitions, thrills and spills to see who emerges on top, but what's clear already is that those with a trusted brand, a 'real world' presence and an online business have a distinct advantage."
Those likely to survive are firms that have built stronger trust, reputations and brands - seen as essential for selling art online in last year's Hiscox report, which also listed returns policies, improved logistical processes, trusted due diligence (condition reports, certificates of authenticity) and more transparency (artist reports, past prices) as key ingredients for success.