I have been doing my own J-cards for some years. I started drawing a template in Macromedia Freehand (which although outdated it’s one of the best design software out there). I have done lots of different J-cards for my kids to help them identify their own cassettes, so they can listen to whatever one when they want, without my help:
Cassette J Card Template

- J-Card, U-Card, and O-Card Templates The traditional packaging for a cassette is a hard plastic box (Norelco box) with inserted printed album art. Our variety of templates allow you to create a unique package for your cassette release.We’ve also re-introduced the O-Card.
- Yeah, you can fit four of a 4'x4' single panel j-card in the middle of an 8.5'x11' sheet of paper/stock. So if you have a run of, say, a hundred tapes, you just have to print out 25 pages, cut em apart, and you're done.
- Templates CD Cassette VHS, Dvd & Blu RaY Poster/Postcard/Flat STICKER VINYL FORMS Merch/Apparel Most Popular. J Card Standard plus5 Panel Preview.

These are some of the custom J-cards I’ve made to my youngest son (3 yr old now). As you can see, most are from the cartoons he like.

Make and print a cover for a cassette tape using this template. Flip-it card templates I have worked up a set of American sized templates with help from two friends out there in the States - as your paper sizes won't work through UK printers so I couldn't test them here, so many thanks for you help again Jane & Kathy.
I have my own templates, but I understand that Freehand is not and easy to use software for everybody (it’s a professional grade design software), so I thought it would be nice if I could make one for the worldwide known MS Word, and I finally did. And I’m giving it to you now for free.
And here you can see some custom stickers I’ve made to my oldest son (8 yr old now). Some have 3-4 years now; some are recent (like the one of Police and Linking Park).
To use it you just need your own MS Word, version 2007 or newer, because it’s not a .doc but a .docx document. It contains a J-card and two different inner stickers with rounded holes or a window.
It’s very easy to use but you need at least a basic knowledge of Word. You can add your own text and an image.
Read the detailed, step-by-step tutorial
[UPDATE 2018-01-29] There’s a new version of the J-card with more options. See it here.Cassette J Card Printing
I’ll be glad if you leave your comments here or in this thread at Stereo2Go. Any feedback is welcomed.