I use Landscape, the default theme at the time of writing.
blog\blog\node_modules\hexo\node_modules\hexo-cli\assets\themes\landscape\_config.yml
At the bottom of the file you will find the "Miscellaneous" section.
# Miscellaneous google_analytics: favicon: blog\themes\landscape\source\css\images\favicon.ico twitter: google_plus: fb_admins: fb_app_id:
Windows can be directional directional when it comes to oblique worms, so try the opposite direction if you are using a PC. This helped me, and I was able to use the .ico file as well as the .png file.
If you still need a placeholder image, I used Favicon.cc and had great results.
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