'Graffiti was first considered just street pictures with not much value. But when given the attention and opportunity, it flourished into a unique form of art.

'For ex-offenders, it's the same - if they are given the opportunity and encouragement, they can flourish and become even better people.'

Among the participants were 10 ex-offenders who have had counselling through the society, while the rest were mainly secondary students.

Under the guidance of French artists Ceet and Kongo, they completed a 10-metre-long work with the theme 'One Love'.

The painting will be showcased at the society's centre in Shan Ha Wai near Pok Hong Estate in Sha Tin.

The training session was part of Le French May, a month-long celebration of French culture in Hong Kong. It was co-organised by the society and the Federation of Women Lawyers.

Yuen said the artists wanted to contribute to building the community and had previously held graffiti sessions with prisoners in Singapore.

Ceet, who is based on Discovery Bay, said they wanted to introduce street art in Hong Kong and thought it would be meaningful to teach teenagers in rehabilitation.

Part of the proceeds from sales of the artists' works will go towards the society.

One of the participants, an ex-offender known only as Siu Chow, 21, said: 'I never thought that I'd have the opportunity to collaborate with such famous artists.'

Siu Chow said that when he was first released from jail in July, he felt worthless and hopeless. But he soon found there were people who cared.

'It makes me feel really warm, knowing that there are people who are going out of their way to care for us. This is what events like this make us feel,' he said.

Yuen said: 'They see this experience as valuable because it is not every day they get to learn graffiti.'

Form Three pupil Holly Hung said she started taking part in events at the society two years ago. The ex-offenders she met were very nice, Holly said. 'They are trying to become better, and I think that we have to accept them,' she said.