Filipino national Arnel Martinez Raymundo, 48, was convicted of attempted murder and voyeurism at Cardiff Crown Court on Thursday.
After the attack on 12 June, Raymundo, of Grangetown, fled to London before being arrested by police.
Recorder of Cardiff Eleri Rees said he faced "a significant" prison sentence.
A jury unanimously found Raymundo guilty of both charges.
The court heard he stabbed Anna Caladiao, 43, in the back 18 times leaving her with "life-threatening injuries" after she found the footage.
Ms Rees called it "quite a distressing case" .
Raymundo must sign the sex offenders register and a victim impact statement will be sought before sentencing on Friday.
Prosecutor James Wilson said that further charges could also follow after other images were discovered.
A man from Cardiff who repeatedly stabbed his girlfriend following a row over footage he had of a woman in the bath has been found guilty.