This app was mentioned in 5 comments, with an average of 1.80 upvotes
Be funky: https://play.google.com/store/apps/details?id=air.com.befunky.BeFunkyPhotoEditor
☝ No sign up needed. Works completely offline
Adobe photoshop express: https://play.google.com/store/apps/details?id=com.adobe.psmobile
☝ Sign up required after installation... but works completely offline after that. I personally recommend this one
Yeah, it took me a pretty decent amount of time to make the best cartoons one. I mean, Young justice, TMNT, Teen Titans, and Avatar were a given, but after that I really had to stress my brain muscles because I don't watch that much non-anime.
About the format. I use this app to make them. It's simple and easy to use, highly recommend.
I now have all the colors of this series - green, yellow, blue, red, and gold and will be posting a picture of them all in one shot later today. beginning to feel a bit better and waiting on my other card display case to get here. If anyone is interested in what program I use for the filters/borders, its beFunky and is free on the Google Play Store https://play.google.com/store/apps/details?id=air.com.befunky.BeFunkyPhotoEditor&hl=en
I usually use BeFunky because I'm on my phone all the time but I suppose you could also use Photoshop.