How much traffic on the website, I can consider as a high
It depends on your webhosting. Most plans have limits.
For example: 10 Tb/ month.
If your hotlinked traffic is using most of your allowed traffic, then you definitely can consider this as “high amount”
For so called “unlimited/unmetered” plans, your webhosting support may send you a warning, if you reach enormous values.
In fact hotlinking pics does not bring you visitors, but is consuming your server resources,
if hotlinked traffic is low, then you dont have to care much, unless you encounter “reddit effect” or something like this, when someone shares a pic from your site on high traffic sites, this may happen anytime and will generate significant increase in resources usage for several hours-days, then cease back to low.
If people constantly share your media on other sites, then using watermarks could be good idea to promote your site name.
If amount of “parasite”-traffic is high – you may need to protect your server resources from being used and forbid hotlinking completely or by referrer, with .htaccess or by other means.
