C.js

/**  
 *  
 * @param {String} imageSrc - ссылка на картинку  
 * @returns {Promise}  
 */
function traceImage(imageSrc) {
  return new Promise((resolve) => {
    const image = new Image();
    image.onload = function () {
      const canvas = document.createElement('canvas');
      canvas.width = image.width;
      canvas.height = image.height;

      const context = canvas.getContext('2d');
      context.drawImage(image, 0, 0);

      const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
      const data = imageData.data;
      let min = 0;
      for (let i = 0; i < data.length; i++) {
        if (data[i] !== 255) {
          min = i;
          break;
        }
      }
      let max = 0;
      for (let i = data.length - 1; i >= 0; i--) {
        if (data[i] !== 255) {
          max = i;
          break;
        }
      }

      min = Math.floor(min / 4);
      max = Math.floor(max / 4);
      minX = min % imageData.width;
      minY = Math.floor(min / imageData.width);
      maxX = max % imageData.width;
      maxY = Math.floor(max / imageData.width);
      const rgb = getAt(minX, minY, imageData).join(', ');
      resolve(
        `<div><div style="  
            position: absolute;  
            width: ${maxX - minX + 1}px;  
            height: ${maxY - minY + 1}px;  
            top: ${minY}px;  
            left: ${minX}px;  
            background-color: rgb(${rgb});"></div>  
      </div>`)


    };
    image.src = imageSrc;
  });

  function getAt(x, y, imageData) {
    const index = (y * imageData.width + x) * 4;
    return [imageData.data[index], imageData.data[index + 1], imageData.data[index + 2]];
  }
}