A total of 350 websites were reported for allegedly featuring videos of sexual abuse, of which Spletno Oko found 45% to indeed feature such images.
The hotline website believes the cases fall under Article 176 of the penal code, which penalises presenting or publicly exhibiting pornographic material featuring minors.
Spletno Oko says that compared to 2017, the number of reports and potential criminal acts related to the sexual abuse of children increased manifold.
It partly attributes the rise to an intensive awareness campaign about child abuse and about the possibility of anonymously reporting it.
The cases were forwarded to the police, and the countries in which the contentious content had appeared, most often the US and Netherlands, were notified of it.
The majority of the cases forwarded to the police featured children aged 11 to 15.
A rise in the share of material with much younger victims, aged up to six years, was also recorded, increasing by 6 percentage points to 14%.
The share of videos showing "severe sexual abuse" content rose by 9 points to 55%, which Spletno Oko says is worrying. The majority of these victims were girls.
Hate speeches mostly related to Muslims and migrants
Internet users moreover reported 591 cases of alleged criminal acts of hate speech, slightly more than the previous year.
Spletno Oko found 35 of these cases to be potentially prosecutable, up 10 from 2017, but the police filed criminal complaints in only 21 cases.
The majority of the cases forwarded to the police (28%) were related to ethnic background, foremost to migrants and Muslims. The majority were found on news portals.
Spletno Oko is part of the Safer Internet Centre and has been receiving reports of sexual abuse videos and hate speech cases on the internet since 2007.