Answer
Add the image(s) to the Graphics section in Report Designer's upper-left panel, drag the image into position on the layout, then in its Properties set it as a Dynamic Image stored on Database, with a SQL statement matching the image type: SELECT IMAGE FROM REPORT_IMAGES WHERE IMAGE_NAME=:1 for a general report image, REPORT_LOGOS for a logo image, or REPORT_SIGNATURES for a signature image. Feed the actual image name into the Bind Variable property, in single quotes. Once the layout is uploaded to the relevant report definition, the image referenced by that exact name also needs to be uploaded separately, with the matching name, on the corresponding tab of the Report Images page — the layout reference and the uploaded image are two separate steps that both need to use the same name.