The thumbnail 1,2,3,4 images are stored in sap.bi.launchpad.db.tables::BI_ITEM_DEFINITION under content column. All the metadata used (type of chart, x-axis, etc...) is stored in this table and during run time of Lumira Launchpad and when you open a story, Lumira gets this metadata and data from database and renders these charts on client side. It also stores last refreshed image into same column.
Without client side processing in recreating these charts , I dont believe to get these charts and display on your UI.
Thanks,
Naresh G