The favicon of a website is the little icon that shows up at the top of the browser tab, next to the title of the web page that you visit in the tab. It is set in the header of the page, using the link "rel="shortcut icon".
Use any graphics tool to design the icon. (We have used Powerpoint,
see lambda1.pptx and lambda2.pptx.)
Keep it simple, and bold. Transparent background looks sleek.
From your graphics tool, export to PNG. If you want to make the
background transparent, use Adobe Photoshop.
For that, open the PNG in Photoshop and
left-click on the Eraser tool. Choose "Magic Eraser Tool". Then click
on all white parts to make them transparent. Save the file.
Transform the PNG to ICO format (32x32 pixels)
gusing the ImageMagick tool convert:
convert -resize x32 -gravity center -crop 32x32+0+0 lambda1_transparent.png lambda1.ico
Copy the ICO file to rails/app/assets/images/favicon.ico.
The Ruby-on-Rails system will find it there and install it in the
right places.
cp lambda1.ico ../../app/assets/images/favicon.ico