There are other websites (
here's one) that let you drop an image to be converted for display on a Honda screen, but I haven't tried them. I'm not sure if the aspect ratios of the wallpaper images they produce will match the Clarity's screen, however. The one I linked says the image must be exactly 840 x 468 pixels, which is a very strange 70:39 aspect ratio, that is probably applicable to older Honda displays.
The Clarity Owners Manual (page 223) says that the minimum image size that will fill the screen is 800 x 480 pixels, but it can accommodate images as large as 4096 x 4096 pixels (with a 5MB limit). Both BMP and JPEG image formats are supported. However, if 800 x 480 fills the screen without black bars at any edges, then the aspect ratio would be 5:3 (as opposed to SDTV's 4:3 or HDTV's 16:9). You want to match the display's aspect ratio to avoid distorting the image.
All you need is a computer with a basic image editor program that can crop the photo and set the resolution of the wallpaper image you want to upload. Then you use a USB drive to load it into your Clarity. I just looked on my Windows 7 computer at Windows Live Photo Gallery and I couldn't find a cropping option, so perhaps that old program is too basic. Equally ancient Photoshop CS2 is now a free download, however.