By Jo Twist BBC News technology reporter

Not all the more than 1,000 members on Flick Off are against the move

The team behind the successful online photo sharing community site, Flickr, has moved to soothe fears over changes to member accounts.

A protest group was set up within the community after it was announced that that from sometime in 2006, users will need a Yahoo account to login.

Many in the Flick Off group of more than 1,000 have threatened to quit their membership if this happens.

It is not what they signed up to, they say. Yahoo bought Flickr in March.

Flickr's founders, Stewart Butterfield and Caterina Fake say there is no ulterior motive for the change, and that it is simply to make it easier to sign up to and technically manage membership.

The only thing that *really* worries me ... is the idea of Yahoo using *my own* stuff for any of their purposes without my consent or without paying any due rights ale2000, Flickr member

The change does not affect on-screen Flickr IDs.

But it means Flickr account holders with no Yahoo login will see their presence and photos disappear in 2006 unless they sign up with Yahoo.

"We care deeply about our community, and their worries are ours," Ms Fake told the BBC News website.

"But I think the fears are unfounded. As always, the proof is in the pudding. We're tending to our knitting, and making sure the Flickr experience is as good as it's always been."

Flickr has grown in popularity since its formal launch in February 2004 and now hosts more than 37m photos and 1.2m members.

'Big company' fear

Although some in the Flick Off are vociferously angry, others have joined the group merely to discuss the changes.

"I didn't pay for a Yahoo account, I paid for a Flickr account. If I wanted a Yahoo account I would have signed up for one," says one member, Jamie Quint.

Recognising its unique qualities as an online community, web giant Yahoo bought Flickr and its parent Ludicorp, in March 2005.

In June, the Vancouver based team which nurtured Flickr moved lock, stock, and servers to Yahoo's California base. This was considered by some as an act of "neo-colonialism".

People are encouraged to "tag" images with keywords

Although the Flickr team has repeatedly reassured members that their on-screen Flickr IDs will not be lost, there are still concerns about where this convergence might lead.

Mr Butterfield told the BBC News website that he was not worried about people leaving the community as a result of the changes.

"It would be unfortunate, but it is not enough of a reason for most people to leave. It is a relatively small number of people," he said.

He indicated too that more than half of the comments were found to have been posted by members representing rival photo sharing services.

But the fracas over the login changes are indicative of the inherent mistrust of behemoths such as Yahoo and the other net giant, Google.

Their worries are that the innovation and agility which characterised Ludicorp will disappear as it becomes "Yahooised".

Others have voiced fears over copyright on their images and whether Yahoo will claim "ownership" in the future.

"The only thing that *really* worries me ... is the idea of Yahoo using *my own* stuff for any of their purposes without my consent or without paying any due rights," says one user, ale2000, posting on the Flick Off group.

The Flickr team deny this would be the case, although the Terms of Use have been altered slightly since Yahoo took over. But Yahoo is battling historical mistakes.

In 1999, when it bought GeoCities, Yahoo announced it owned all the web pages, articles, and images on member sites and had "irrevocable" rights to them for all time.

But Mr Butterfield said Yahoo had learned from its early errors, and stressed that the new terms of use on the site were more formal and legalistic, but still made it clear that Yahoo does not own the images.

"There is a large community of web users who have a trust issue with Yahoo," said Mr Butterfield. "But the Yahoo of 1995 is not the Yahoo of 2005."

He said, however, that historical mistakes and Yahoo's reputation for being ad-friendly would mean some people would not like it no matter what.

Flickr encourages the application of Creative Commons licences to images, however, and there are more than 4.5m images which have applied them.

These are free licence agreements, the terms of which are decided by members.

'Social fictions'

The protest group reflects Flickr's powerful "community feel", which has been one the main reasons it gathered such a loyal following in such a short time.

Flickr's roots were as a massively multiplayer online game called The Game Neverending where conversations around "objects", such as images, were encouraged.

Some describe it as "massively multiplayer online photo sharing." It encourages people to "tag" their photos with keywords so that people can search for themes, such as cats.

Anyone can create themed pools or groups and users can post images straight onto blogs from Flickr.

It is this informal, independent "community feel" with which many Flickr members pride themselves. Many feel this independence is gradually being taken away, bit by bit.

They fear the "big corporate" take over threatens that sense of being part of something special.

Colr Pickr is an example of how people have used Flickr's API

"I'm not cross and I'm not bitter - I'm just a little sad because I have a belief that things can be good/great without taking the obvious route", comments one user, grange85.

But, Ms Fake said, the Flickr team at Yahoo was still committed to what its members value about the site.

"We listen to our users, are honest with them, always have been, always will be. We hear their concerns. We haven't screwed up Flickr, and we won't," she said.

Clay Shirky, commentator and writer on the social aspects of the net, told the BBC News website he had seen it all before.

He said it was part of a "social fiction" that members of a community online build when they form an emotional connection to the place.

"The social fiction of the group is essential," he told the BBC News website.

"Actions like a change in rules, all that does is remind people of the truth - you don't own the infrastructure. But that makes people hysterical."

He continued: "These things boil over not because there is a particular issue, but the sale [Flickr sale to Yahoo] means the real world has intruded on their world.

"What happens in any well managed transitions is that the operators offer reassurance and say they don't want to make it an unpleasant place to come."