github_img_to_canvas.js

Array.from(document.querySelectorAll("img[src^=\"https://private-user-images.githubusercontent.com/\"]")).forEach((img, index, array)=>{
    if(img.complete) {
        var anchor = img.parentElement;
        anchor.removeAttribute("href")
        // console.log(img)
        var canvas = document.createElement("canvas")
        canvas.height = img.naturalHeight
        canvas.width = img.naturalWidth
        canvas.style.maxWidth = "100%"
        var context = canvas.getContext("2d")
        context.drawImage(img, 0, 0)
        anchor.appendChild(canvas)
        anchor.removeChild(img)
    }
})

github_img_to_canvas.min.js

javascript:Array.from(document.querySelectorAll('img[src^="https://private-user-images.githubusercontent.com/"]')).forEach((img,index,array)=>{if(img.complete){var anchor=img.parentElement;anchor.removeAttribute("href");var canvas=document.createElement("canvas"),context;canvas.height=img.naturalHeight,canvas.width=img.naturalWidth,canvas.style.maxWidth="100%",canvas.getContext("2d").drawImage(img,0,0),anchor.appendChild(canvas),anchor.removeChild(img)}});