The legacy responsive image format which is deprecated since CoreMedia 7 is no longer supported by the responsive images JavaScript of the Frontend Workspace. In case you did not make any customizations to the responsive images format and use the function responsiveImageLinksData of the BlueprintFreemarkerFacade there is nothing to do.

Old Format:

<img src="image3x1.jpg" class="cm-media--responsive" data-cm-responsive-media='{
  "3x1": {
    "320": "image3x1_small.jpg",
    "640": "image_medium.jpg",
    "1024": "image_large.jpg"
  },
  "2x1": {
    "200": "image2x1_small.jpg",
    "400": "image2x1_other.jpg"
  }
}' />

New Format:

<img src="image3x1.jpg" class="cm-image--responsive" data-cm-responsive-image='[
  {
    "name" : "3x1",
    "ratioWidth" : 3,
    "ratioHeight" : 1,
    "linksForWidth" : {
      "320": "image3x1_small.jpg",
      "640": "image_medium.jpg",
      "1024": "image_large.jpg"
    }
  },
  {
    "name" : "2x1",
    "ratioWidth" : 2,
    "ratioHeight" : 1,
    "linksForWidth" : {
      "200": "image2x1_small.jpg",
      "400": "image2x1_other.jpg"
    }
  }
]' />

(CMS-14766)