A man has been arrested after he allegedly altered stolen images of teenage girls to be sexually explicit and posted them to adult websites.

Detective Senior Sergeant Ciaran Sloan said the 56-year-old predominantly targeted teen girls from the Marlborough area.

Investigators traveled to Nelson and located the man.

"This type of crime is extremely upsetting for those affected by it and I am glad we have been able to stop this person from causing more harm," he said.

The man has been charged with causing digital harm, possession of objectionable material and child exploitation and is due to appear in the Nelson District Court on May 23.

If you have been affected by this type of behaviour, you can report it to police on 105 so it can be investigated.

Marlborough residents can give information directly to Detective Glen Lindup at the Blenheim Police Station.