A demo script to get the image of the shape group in active worksheet.

Get image of shape group.EXCEL.yaml

name: Get image of shape group
description: A demo script to get the image of the shape group in active worksheet.
host: EXCEL
api_set: {}
script:
  content: |
    $("#run").click(() => tryCatch(run));

    async function run() {
      await Excel.run(async (context) => {
        // if a chart is selected, get the image of chart
        // else if a range is selected, get the image of range
        // else // get the image of a shape group in active worksheet
        const sheet = context.workbook.worksheets.getActiveWorksheet();
        let shapes = sheet.shapes.load("items");
        await context.sync();

        let image;
        for (let i = 0; i < shapes.items.length; i++) {
          if (shapes.items[i].type == Excel.ShapeType.group) {
            image = shapes.items[i].getAsImage(Excel.PictureFormat.png);
            break;
          }
        }

        await context.sync();

        $("#content-main").html('<img src="data:image/png;base64,' + image.value + '" style="background-color:black;" />');
      });
    }

    /** Default helper for invoking an action and handling errors. */
    async function tryCatch(callback) {
      try {
        await callback();
      } catch (error) {
        // Note: In a production add-in, you'd want to notify the user through your add-in's UI.
        console.error(error);
      }
    }
  language: typescript
template:
  content: |-
    <button id="run" class="ms-Button">
        <span class="ms-Button-label">Run</span>
    </button>
    <h2>Show image blow:</h2>
    <div id="content-main"></div>
  language: html
style:
  content: |-
    section.samples {
        margin-top: 20px;
    }

    section.samples .ms-Button, section.setup .ms-Button {
        display: block;
        margin-bottom: 5px;
        margin-left: 20px;
        min-width: 80px;
    }
  language: css
libraries: |
  https://appsforoffice.microsoft.com/lib/1/hosted/office.js
  @types/office-js

  office-ui-fabric-js@1.4.0/dist/css/fabric.min.css
  office-ui-fabric-js@1.4.0/dist/css/fabric.components.min.css

  core-js@2.4.1/client/core.min.js
  @types/core-js

  jquery@3.1.1
  @types/jquery@3.3.1