http://base64online.org/encode/

usage en javascript :

window.ImgCollapsed = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABwAAAALCAYAAABs3u23AAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAAAYdEVYdFNvZnR3YXJlAHBhaW50Lm5ldCA0LjAuNvyMY98AAACtSURBVDhPY/j//z9dMZjYcOjK/9rZO3BikDyyJkowmAAZig9A5TE0k4PBBMjAP3/+wDEDUBjG/vb1A20s/PbtKxyDLATRHz+8/P/gwT0aWQj0CcgidHz31kWcFhobG/8HYWL5IAwmQAZ+/PgWjN++eQa26OXLx2Df3bx6mjYWvnh2A2w4CIMsvHbh2P9LZ/b/P3NyF22CFGTw/r0b/h/asRwDU91CuudD+uH/DADncY0ihCIzIAAAAABJRU5ErkJggg==";