The number of women being sent sexually explicit images by strangers on trains is going largely unreported despite a spike in incidents.
Reports of cyber-flashing to British Transport Police have almost doubled in a year, although campaigners say the number of women affected "will almost certainly be much higher". Despite the rise there was only one arrest in 2019.
Cyber-flashing is when a person is sent an unsolicited sexual image on their device by a stranger nearby through AirDrop, a file-sharing function on iPhones.
Victims - often targeted on trains due to the technology's short range - said it caused them to feel fearful on public transport.
Figures show incidents more than doubled year-on-year in 2016, 2017 and 2018.
In 2019, there were some 66 reports of cyber-flashing - almost double 34 reports in 2018, and a large jump since 2016, when three incidents were reported.
Although numbers have leapt year-on-year, police believe it is still going under-reported due to victims believing the incident is "not serious enough" to speak to officers.
If a person's AirDrop settings are set to "Everyone", it means someone outside of their contacts list can request to send them a file.
This can be done anonymously, as all that is shown on the receiving device is a preview of the picture and the name of the iPhone sending the file.
Judith Rita, 21, got on a train at Finchley Road Station last year when she received an AirDrop notification with an obscene picture.
"My initial reaction was fear mixed with disgust, why would someone do that?," she said.
"I hit decline straight away and tried to find the culprit, but the freakiest thing about it is that you don't know, as almost everyone is using their phone...at some point the thought occurred that whoever it was may not even know who they sent it to.
"I guess in that moment they had twisted my hand and forced me into embarrassment, despite me having no wrongdoing.
"I was just angry, annoyed and creeped out not knowing who was watching me."
Detective Inspector Ashley Cooper, from BTP, advised people to review their AirDrop settings to only receive messages from people in their contacts list.