I made a little tool that will help you to create your own cards. You can check it out on the following link:Alteil Card Maker
This tool is made with HTML5 so you will need a modern browser (browsers like internet explorer 9 or before won't work).
Once you finish editing your card click on the the "View as image" button and a new tab will be opened with an image of your card. To download your card right click on it and press "Save As".
The optimal image size is 200 x 280, so use at least an image with that size or with a similar aspect ratio of width to height.