I tested this with a card other than a credit card and it is accurate. However, I tested it with wifi off to see if it is using the Internet and it did use 24 KB of data, which would only be enough data for a very low resolution picture to be sent. To gain trust of the users, you may not want to have the app use data. Users should be sure not to use any cards with personal info.

It took many tries to figure out how to use this. Once you realize you need to push the plus sign to measure something, whether it's a box or line, after you've encircled the CC, it will work. If you are not directly over the object to be measured when taking the photo, boxes won't measure accurately. If you need a measurement without having a tape measure or ruler, it can be a great help, but I'd try to be on wifi if you could.

Should be more useful if the app can automatically locate the card and attach the box(the given one).

Although it is not working perfectly at the moment, I am giving it 5 stars for the innovative idea and hoping for the updates for improvement!