What’s wrong with this block of mine for the grayscale effect?
Is your image stored in the assets? The assets are read only… try to copy the file to ASD and then try again…
use the companion app together with Do it to debug your blocks, see also tip 4 here App Inventor: How to Learn | Pura Vida Apps
see also Live Development, Testing and Debugging
Taifun
My images are stored in Firebase.