This filter can be used to set custom user avatar(profile) image just prior to display.

Hook Type: Filter
Source: core/classes/class.arm_global_settings.php
add_filter( 'arm_change_user_avatar', 'your_function', 10, 5);
function your_function($avatar, $id_or_email, $size, $default, $alt) {
    //Filter user avatar.
    if ($id_or_email == '26') {
        //pass your custom image url in src.
        $avatar = ''.$alt.'';
    return $avatar;
Whole img tag to be returned
user id or email address
Image height and width
Default Avtar image tag
Image alt value