I can not find, where to set the “default_image” for dynamic pages: archive, search, not found etc.
The only way to achive this was to rename my own image to glasses.jpg and replace the one delivered with the theme.
Is there another way?
If by “default_image” you refer to the default header image, that’s configurable in WordPress’ Header Image controls (in the customizer we’re moving that under Site Identity, but the Appearance > Header menu item takes you there directly).