Hidden items will not be rendered in the CSV document. The purpose of the CSV rendering is to recreate the data layout of the report - Design Considerations for CSV Rendering
Thus my suggestion is to use the Checkbox
item, which is rendered in the CSV as 0 or 1 (depending on the value) and the Checkbox.Text,
if any. To make the Checkbox item display images in the report you can use its Checked/Uncheked/IndeterminateImage
Let us know if you need any further help.
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