iConvert is a free to use web utility, which does not require registration, which can convert any of the supported image formats to icons adapted for Windows , Linux or Mac
Supported input formats are many, including the most popular, as ico, png, svg, cur, tif, xpm, rsrc, tga, icns, bmp, jpg or gif. We just have to indicate their local route by clicking on browse button and click the “Convert “icon.
We can convert images to icons icns (Mac OS X), icons ico (Windows), icons PNG ( iPhone), icons favicon (WWW), icons PNG (Linux), support icons Finder (Mac OS X), 32-bit icons, 8-bit icons (PNG), 4-bit icons (PNG), 1-bit icons, etc..
Link : iConvertIcons