Siemens no longer include panel images for their range of HMI panels in the standard TIA Portal installation.
Instead these will need to be downloaded from the following link - Image Downloads for SIMATIC HMI Operator Panels: Comfort / Mobile / Basic Panels - ID: 109825750 - Industry Support Siemens
Please ensure you select the appropriate files for your version of TIA Portal.
After installation of the downloaded files you should be able to continue with uploading to your HMI panel.