This program can convert most modern graphics into a form compatible with the Apple2 HGR bitmap mode. It supports a drag-and-drop interface and handles resizing and scaling, several forms of user-configurable dithering, adjustable color selection, and more.
The resulting file can be saved as a raw binary in HGR format, or as a DOS3.3 (bootable) disk image, or as a PNG if you want to look at it on the PC again.
It is based on my Convert9918 tool and has many of the same features. It renders the image as close as possible to how hardware will display it, and will not generate illegal color combinations.