I don't know if you can "create an image" in PHP [not my area of expertise], but you can store a complete image in an HTML image tag. So, if you're using the same image for each response (server online = green happy face, server offline = red sad face), then you can store the image as text within the HTML tag. The following example is a sad red square face, about 67 pixels square.
Several on-line converters are available. Searching for "Image to Data URI converter" should provide a tool to use.
<img src="data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEAYABgAAD/4QBmRXhpZgAATU0AKgAAAAgABgESAAMAAAABAAEAAAMBAAUAAAABAAAAVgMDAAEAAAABAAAAAFEQAAEAAAABAQAAAFERAAQAAAABAAAOw1ESAAQAAAABAAAOwwAAAAAAAYagAACxj//bAEMAAgEBAgEBAgICAgICAgIDBQMDAwMDBgQEAwUHBgcHBwYHBwgJCwkICAoIBwcKDQoKCwwMDAwHCQ4PDQwOCwwMDP/bAEMBAgICAwMDBgMDBgwIBwgMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDP/AABEIAEMAQAMBIgACEQEDEQH/xAAfAAABBQEBAQEBAQAAAAAAAAAAAQIDBAUGBwgJCgv/xAC1EAACAQMDAgQDBQUEBAAAAX0BAgMABBEFEiExQQYTUWEHInEUMoGRoQgjQrHBFVLR8CQzYnKCCQoWFxgZGiUmJygpKjQ1Njc4OTpDREVGR0hJSlNUVVZXWFlaY2RlZmdoaWpzdHV2d3h5eoOEhYaHiImKkpOUlZaXmJmaoqOkpaanqKmqsrO0tba3uLm6wsPExcbHyMnK0tPU1dbX2Nna4eLj5OXm5+jp6vHy8/T19vf4+fr/xAAfAQADAQEBAQEBAQEBAAAAAAAAAQIDBAUGBwgJCgv/xAC1EQACAQIEBAMEBwUEBAABAncAAQIDEQQFITEGEkFRB2FxEyIygQgUQpGhscEJIzNS8BVictEKFiQ04SXxFxgZGiYnKCkqNTY3ODk6Q0RFRkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqCg4SFhoeIiYqSk5SVlpeYmZqio6Slpqeoqaqys7S1tre4ubrCw8TFxsfIycrS09TV1tfY2dri4+Tl5ufo6ery8/T19vf4+fr/2gAMAwEAAhEDEQA/APmunLBI8TSKjGNMBmA4XPqabX7YfsUftF/syWP/AAT20HwzqPiLwDoumtoqp4l0TVb6CG8u70RKbqVoWbzZneRdyMgJOECYKhV/F8qy2OMnKEqihZX16/l/XQ/1b8R+O6/C+Eo4qhgqmK9pNRahf3Va7btGWvSKsk3vJdfxPoooryz9FCikY17L/wAE+/Avgb4lftg+CdF+JFwtv4Qvrxxd+ZKYY53ETtDE7jlUeYRox4+Vj8y/eGlGk6tSNNaczS1217nn5tmMMvwNbHVIuUaUJTairyaim2orq3ayXVnjdFfqd/wXv/Zg+GPwm+Bvg/xJ4Y8NeG/CviafXE0wQaVbQ2K3ln9nuJHYwxgBtkiwjeBx5gBJyuPyxzXZmeXywVd0JtNq2q8z5rw/42w/FeTQznDU5U4yclyytdOLs9Vo15hRRRXnn2oUVa0bRbzxHqtvYafaXV9fXkgigt7eJpZZnPAVVUEsT6AZr6U+F3/BHb9oL4pQyTR+BZtBgQA79buY7Fmz2CMfM/8AHcCujD4WtXdqMHL0TZ4uc8SZTlEFUzTE06Ke3POMb+l2r/I+YT0oB4r6U+JX/BIn9oP4ZXZjm+HuoazDsMgn0aaO/RgOowjFwfYqCe2a+ddb0K+8Mavc6fqVndafqFnIYri2uYmimgccFXRgCrD0IzRXwtai7VoOPqmh5RxFlWax58sxNOst3yTjK3rZu3zKppp9KcTxTRXOeyOr6q/4Jbf8E5Zv27viVfTa5Jqul+A/D8eb++tECvdXB27LWJ2BUMVJdjhtqgcAupr5Vr9+/wDgkZ8G4/gv+wP4Gt/s81ve+ILdtevBKu1mkuTuQ47DyREB7AV9Bw3lsMZi+Wr8MVd+fZH4n488e4nhfhv2uXy5a9aSpwfWOjcpLzSVl2bT6HpnwB/ZB+Gv7MGiw2fgjwho+itCpU3gh82+mz94vcPmVs+hbA6AAcVB8bP20/hT+znqf2Hxp468P6FqHlmY2ck/m3QTAOTFGGcZzxkfN2zX5y/8FsP+Ci3jCw+Otx8LvBHiG88P6P4ethFrFxpd40c2ozzIjtE7rgqsa4Xap5LuG9B+b9/f3Gq3stzdTTXFxOxeSWVy7yMepJPJJ9TX0uY8UU8JN4bB017rt2Wm9kv+AfgnA/0d8dxNhaWf8TY2a9vHnUV71RqWsXKc7pXWtrS0au07o/o7+D/7aXwp+PuvtpPg/wAfeG9c1RU8wWcF0FuHXnlUbDNjHO0HHfGa5P8Abv8A2B/B/wC2p8LNUtb7SdPt/GMVo39ja4sSpdW06qTGjyAbmhLcMhyMEkYYAj+fHTNTuNF1GC8s7ia1urWRZYZoXKSROpyGVhyCDyCK/oJ/4JkftSal+15+yD4f8Va55Z8QQSzaZqckahUnnhbHmBR90uhRiOMMxwMYrpyjOoZqpYTFQV7X8mvns0eF4meE2L8OZYfiPh/FzcFNRu7KcZWuruNlKMrNNWVtE7p6fgL8RPAOrfCvx1q/hrXrN9P1nQruSyvbdyCYpY2KsMjgjI4IyCMEcGsdTX3p/wAHAHwCvfAn7Vtj44jtY10bxxp0a+fEm3N3bKI5Ff8A2jH5JB4yCf7pr4KAr89zDBvC4mdB/Zf4dH9x/bXA/E0OIMhwucQterBOSWqUtpx+Uk18h9frl8CP+C9nw28Hfsw6HaeINH8Sf8JpoGlRWD6fa26G3v5Yo1jV0mLAIj4BO4ZTLABsDd+RtFbZdmmIwUpSoNe8rO6uefx14c5NxbRo0M4jJqlLmjyy5Xro0/J2V+umjR0HxV+JerfGX4k654r1yf7Tq/iG9lv7uTGAXkYsQB0CjOABwAAK5+iivPlJyfNLdn2tCjTo040aSUYxSSS0SS0SXkkFfXH/AASk/wCCkP8Aww18QNQ03xMdUvvh94hXddW1oBI9hdjaFukRiM/KuxwCCV2nkoAfkeitsJiqmGqqtSdmjx+JeG8Bn2W1cqzKHNSqKz6NdU0+jT1T7n3B/wAFgf8AgpP4T/bcj8J6B4Js9UGjeHJpry4vr+EQtdTSKqqsaZJCqobJbBJboAuT8PFc0tFVjcZVxVZ16u7/AOGMOE+FcBw5ldPKMtTVKne13dttuTbfdtvol0SsFFFFcp9IFFFFABRRRQAUUUUAf//Z" alt="" />