My daughter is trying to find an image of a sunflower seed with a transparent background right now. I showed her the "filetype:png" trick in google image search to get PNG only results.<p>However, it seems that in the past few years the results are getting less and less reliable. Images now show checkerboard backgrounds to indicate they are "transparent" but in actuality, they are not transparent. They have an opaque checkerboard background.<p>Is there an image search service that shows transparent image results, testing the transparency is true before presenting results?
This is a little indirect, but if you have Photoshop or The Gimp, you can use the selection tool, invert it, and then delete the background, which leaves you with the foreground only, and a transparent background.
Google has an option to include transparent images under the tools option within an image search.<p>Beyond that, it's up to you to actually go to the indicated site, find the image and see if it's publicly available.