Spain has been urged to take a tougher line on sexual predators who take photographs underneath women's clothes without consent after a man was accused of taking such images of more than 500 women and girls.
Spanish police this week announced the arrest of a 53-year-old Colombian man accused of making covert recordings of victims including children and posting them onto pornographic websites.
However, legal experts and rights groups said such abuses were not always taken seriously by police and prosecutors and new laws were needed to protect victims.
"Upskirting and other forms of tech-related invasions of privacy are a growing and urgent problem and a form of violence against women," said Heather Barr from the women's rights division at Human Rights Watch.
"The protections that currently exist are inadequate in most countries — laws and policies simply haven't caught up to how technology is changing the forms violence against women takes."
Spain's justice ministry was not available for comment.
The legal position on upskirting varies considerably across Europe with different countries treating it as a sexual abuse, voyeurism, cybercrime, or no crime at all, said a spokeswoman for the pan-European firm Giambrone Law.
There is no specific law against upskirting in Spain, but it could be prosecuted as a breach of privacy or as sexual abuse, a wide-ranging offence coving non-violent sexual crimes.
However, there is relatively low awareness and it may be treated as a "a bit trivial" or "a prank", said Hannah Wilson, a lawyer with the legal rights organisation Women's Link Worldwide in Madrid.
"It's really important that the law is adapting to these kinds of offences ... and it is being seen by the courts as something that is serious and is a sexual offence," she said.
Spanish commissions examining upskirting have found some judges argue that women who choose to wear a skirt leave themselves open to such assaults, said Deborah Madden, a Hispanic studies lecturer at Manchester University in Britain.
"Legislation that explicitly criminalises upskirting is needed," she said.
"Both the wording and application of legislation related to sex crimes in Spain is undoubtedly outdated and, in my view, reflects a 'victim blaming' culture."
Britain introduced new laws earlier this year to close loopholes in the law and make upskirting a crime, while France is planning to bring in similar legislation shortly.
In Germany and Italy, it is considered a minor offence unless it is accompanied by touching or wider distribution of the images to others, said the Giambrone Law spokeswoman. Activists in Germany are campaigning to bring in new laws against upskirting, but the Justice Ministry has indicated no immediate changes are planned.