I open an empty gray seed packet .png file I made as the base in a pixel/image editor, download the pic I want from the Wiki and open it, copy n' paste it to a new layer in the empty seed packet, resize the wiki pic to fit nicely, recolor the gray seed packet layer to something that complements the pic color nicely, merge the layers, save as a .png to preserve the clear alpha channel. And I've done it enough that I can make a new seed packet faster than it took me to type that, lol!
Edit! Have some new seeds, these are my faves:
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