Hi Jill, There is no harm in getting started on selling images as cards but do price your costs out carefully. I did some research and purchased various photo cards from many different outlets and I was amazed at the variation in costs. Some of the prices quoted I could not match to even make the card. Time is the biggest element in the construction costs. In terms of outlets one of the easiest to get into is the Garden centre market, all you need to provide wall racks or spinners to display the cards then go in regularly and change the display do a stock-take then charge for what they have sold, but the margins are slim and you need to be selling about 50 per week to justify the cost. Galleries on the other hand are very useful places to get them into because if the owner likes the cards you may get the opportunity to sell larger prints and even get an exhibition into the gallery at some time.
Then of course there is e-bay and this does seem to be an area to develop along with your own web-site and mail order offering, a pack of 5 cards will cost about 72p to post first class so this is not off putting to the purchaser.
personally I think get cracking at it and look at all avenues to sell them why not even consider getting a pitch at a street market once a month, even of you do not sell any at the time make sure you give out leaflets with your details and if possible capture their e-mails.
Good luck.
Regards
David