I would suggest the free software from kronocard.com.
The software straightens the cards for you. It can also organize and list to sites. A lot of times I just use it to scan the cards and then take the scans to where I need them since I can do multiples quickly as it finds the edges and straightens while still leaving space around the card to clearly see the edges.
Here is a video about the software:
https://www.youtube.com/watch?v=58K6ykJDTzY