In order to be sure you are not breaking any copyright/trademark laws:
1. Source a reputable image provider that works with artists and pays them a royalty for you. Check out these sites for affordable licensing and subscription/individual image pricing options:
2. Contact image providers and be very clear in what your usage will be, how your products will be made and how it will be distributed. (in some cases they will have the information on subscriptions needed, for your use, right on their websites)
3. Make sure you are choosing the correct licensing subscription for your use and how long you will need to be covered for. You can often choose from individual image purchases to one or two year subscriptions.
Once you have the correct licensing needed for your projects, you can start creating fabulous gifts, greeting cards and more.