With the release of iOS 8, the recommended size is now 180×180 pixels.
For Prestashop, add this line to header.tpl and save the file to image directory
<link rel="apple-touch-icon" href="/img/apple-touch-icon.png?{$img_update_time}" />
Source:
https://realfavicongenerator.net/blog/apple-touch-icon-the-good-the-bad-the-ugly/
http://www.ravelrumba.com/blog/android-apple-touch-icon/