If you look at the description at bottom left it doesn't mention PICTs - I did warn you 😟 - some of us have large numbers of PICTS which was Apple's standard image format at one time, but...
You could look at these: I have no idea whether they are any good or whether they will condescend to convert PICTs, but at least they are free and as they are in the App Store they should be safe.
https://itunes.apple.com/us/app/xnconvert/id436203431?mt=12
https://itunes.apple.com/us/app/pixillion-image-converter-free/id1087406861?mt=1 2
Google throws up some others - one at least is from Softonic and I should avoid that: that and similar sites have been known to add malware. If an app isn't in the App Store get it from the developer's site only.
Think about Graphic Converter - if you are going to do any serious amount of image work it's the best app available. (I have no connection with Herr Lemke, I have just used the program for years).