Generates favicon from static file using Imager. More info: http://craftsnippets.com/articles/adding-favicons-to-craft-cms-website#generating-favicon-from-static-image

favicon_imager.twig

{# v1 #}
{# settings #}
{% set faviconFileName = '/static/images/favicon.jpg' %}
{% set sizesIcon = [192, 48, 32, 16] %}
{% set sizesAppleTouch = [180] %}
{# output #}
{% if craft.app.plugins.isPluginEnabled('imager') and craft.imager.transformImage(faviconFileName, {}, null, {suppressExceptions : true}) %}
{% for faviconSize in sizesIcon %}
{% set faviconTransform = {
    width: faviconSize,
    height: faviconSize,
    quality: 100,
    position: 'center-center',
    format: 'png',
} %}
{{tag('link', {
    rel: 'icon',
    sizes: faviconSize ~ 'x' ~ faviconSize,
    type: 'image/png',
    href: craft.imager.transformImage(faviconFileName, faviconTransform, null, {suppressExceptions : true}),
})}}
{% endfor %}
{# link touch icon #}
{% for faviconSize in sizesAppleTouch %}
{% set faviconTransform = {
    width: faviconSize,
    height: faviconSize,
    quality: 100,
    position: 'center-center',
    format: 'png',
} %}
{{tag('link', {
    rel: 'apple-touch-icon',
    sizes: faviconSize ~ 'x' ~ faviconSize,
    href: craft.imager.transformImage(faviconFileName, faviconTransform, null, {suppressExceptions : true}),
})}}
{% endfor %}
{% endif %}