Convert your image to .ico (use https://hnet.com/png-to-ico/)
Rename your ico to favicon
add this to the <head>: <link rel="shortcut icon" type="image/x-icon" href="favicon.ico" />
<head>
<link rel="icon" href="YOUR IMAGE">
</head>
<head>
<link rel="shortcut icon" type="image/x-icon" href="yourimagehere">
</head>
*supported files are .ico .png or .gif