The plant pictured is hard to see clearly since it's not quite in focus, but it doesn't look like a clover. In either case, to preserve leaves, they are usually pressed. That entails flattening and drying the leaf between two heavy or cinched-together objects, either an actual plant press or a makeshift press using one or two heavy books, newspaper or blotting paper (to absorb moisture; watercolor paper might work), and a place to put it for about week undisturbed so the leaf can dry and stay flat. Pressed leaves fade in color, sooner or later, so a vibrant green leaf will tend to turn a muddy yellowish- or brownish-olive green. They are also brittle and easy to crack or crumble, so it could be protected with some sort of laminate, clear cover, or some other layer.

Miri