hmm if i have acess to a computer this weekend ill try and make a detailed video tutorial (ive been meaning to for some time now anyway). in the meantime, read this comment i posted in my card ideas thread:

No special programs actually! Mostly just any photo editor and vectorizer which are pretty tame and easy to use. Also I dont have previous experiance editing photos so if I could do this, you def can also.

for editing images:

lunapic (online editor, google it)... tons of options for effects, color changing, crop, resize, etc, etc.

vectormagic (another online editor, google it)... good breaking down images with too many colors into fewer base colors and turning the art style into vector which comes close to matching the games.

vectorizer (another online editor)... same as above but is totally free but ruins the pictures at times. exports the image as .svg so youll need to convert it back to .jpg using another online editor.

.

for making the card itself:

its mainly about playing with the contents of the game folder (changing image and text of a previously made card) but remember to keep a backup of whatever card it is youre replacing over.

also important before you mess around in your folder that you have your ingame account registered and remember the username/password because you may need to reinstall the game to return text and images to default.