I recently did this. I searched for pics of what I was looking for then enlarged them then printed them out on regular puter paper. Then traced over them with my special iron on pencil only to find that the puter paper does not work for iron on transfers. Not a big problem I went to walfart and got a tablet of tracing paper retraced the pics onto the tracing paper then ironed them on my quilt blocks. Then painted the outlines and filled in a few small details. Used aunt martha's tube liquid embrodiery paints. Which are very washable but not good for filling in a large area as the paint tends to get stiff. I have pillow cases I painted with simular paints more than 40 yrs ago the paint has faded a bit but you can still clearly see what was painted on the pillow cases and they was well used.
I will add that the simpler your pic the easier it will be. I used the clip art and enlarged it up to printer paper size pics which made the pics very very grainy. Did not matter since all I needed was the simple outlines and a few details.
NOW to FINISH the project lol
