Pixel Size(smaller means more data):
Input Text:

Encode DataSave as Image
Upload encoded image:
Decode Data
Read from image script(replace https://your/url/here):
var image=new Image,canvas=document.createElement("canvas"),ctx=canvas.getContext("2d",{willReadFrequently:!0});function decodeText(e,a){for(var t="",r=0;r<e;r++){var n=Array.from(ctx.getImageData(r%a,Math.floor(r/a),1,1).data);t+=(255!=n[0]?String.fromCharCode(n[0]):"")+(255!=n[1]?String.fromCharCode(n[1]):"")+(255!=n[2]?String.fromCharCode(n[2]):""),255!=n[0]&&255!=n[1]&&255!=n[2]||(r=e+1)}return t}image.src="https://your/url/here",image.crossOrigin="annonymous",image.onload=function(){canvas.width=image.width,canvas.height=image.height;var e=image.width*image.height,a=image.width;ctx.drawImage(image,0,0),console.log(decodeText(e,a))};