1. Go to onMessage > Content > Text.
  2. Click on the gear icon to edit the category's settings.
  3. Enter a number next to Max # of Images to set how many images the text category will support.
  4. Select Allow captions on images (optional).
  5. The Standard image size is set by default. Enable the additional Zoom, Thumb photo sizes (optional). 
  6. Adjust the Max Width and Max Height for the photos (optional)
  7. Click Save & Edit Text.
  8. Add the photo(s) to Drag Images Here.
  9. Click Save.