When only the best quality will do, you're going to need an image in PNG format. Short for "Portable Network Graphics", this is a format that allows you download really crisp images that don't lose detail in compression. That makes them especially good for things like diagrams, graphics, and logos, or for pictures that you're going to do some serious editing on later.
PNG Images Are Perfect for Logos, Designs, and Detailled Images
The downside to PNG images is that because they retain so much quality, they can be pretty big files. This means PNGs aren't the best choice if you want to upload the image to another service (like your blog) but if you want to edit them, they're perfect! Any of the images you download from PikWizard can be downloaded, edited, and used (even commercially) for free, so if PNG is perfect for you, go right ahead!