Keep in mind that there are already many handmade greetings cards available. To be really successful, you need to offer something a little different. In many areas, the market is swamped with handmade cards. An example of a niche is a "green" handmade card business where all products used are recycled, sustainably sourced, or some portion of proceeds benefit ecology projects around the world. When you are thinking about a niche, a great place to start is to think about the things that inspire you or make you smile. 
Cover Verse: An Irish Blessing May the road rise up to meet you, May the wind be always at your back, May the sun shine warm upon your face And the rains fall soft upon your fields, And, until we meet again, May God hold you in the hollow of His hand. Inside Verse: God bless you with the joy of His presence and the gift of His love on St. Patrick's Day and always.
This card has optional greetings: Merry Christmas!, Season's Greetings!, Happy Holidays!, Happy Christmas!, Happy New Year!, Have an Ice Day!, Thank You!, Celebrate!, Happy Solstice!, Happy Birthday!, Happy Belated Birthday!, Happy Anniversary!, Happy Valentine's Day!, I Love You!, Get Well Soon!, Congratulations!, You're Invited!, Come to the Party!, Just Saying Hi!, Thinking of You!, [No Caption]
Have I made my point yet?  They are not kidding when they say bioDIVERSITY.  There is literally every form of living thing available to choose from.  Butterflies and water fowl, more frogs, turtles and lizards than I ever knew existed.  Weird fancy pigeons, big and small game animals…it just goes on and on and on.  The only bad part is you can’t search for specific images but hey, it’s free!