Use PosterMaker.com to create your own greeting cards. You can add images of the city or country you want to make a greeting card of and then add the text "Greetings from...".
Greeting cards have a typical size of 4“ x 6“. The aspect ratio is 2x3 or 3x2 (landscape or portrait). A good format to start your design with would be 1800x1200 or 1200x1800.
Tips and Tricks
Some tips and tricks for making greeting cards on PosterMaker.com:
You can add text to your creation in any font and color you like, optionally with a stroke, drop shadow or background color. Even curved and warped text is available.