I use default WordPress functions to insert images very often. Functions like the_post_thumbnail or wp_get_attachment_image are used in almost every project I do.

By default WordPress adds a title to all of the images printed by these functions, and the title usually is nothing more than the filename.

The result is a lot of title attributes which are pretty much useless and just distracting (while hovering an image for instance).

But thankfully WordPress filters saves us as they often do.

Filter wp_get_attachment_image_attributes and unset the title attribute.

function mytheme_wp_get_attachment_image_attributes( $attr ) {

unset($attr['title']);

 return $attr;
}
add_filter( 'wp_get_attachment_image_attributes', 'mytheme_wp_get_attachment_image_attributes' );

After that you should be set!