very reluctant to reply to this thread!
keyplr REALLY? (rhetorical)
1) your most recent post does not include the most recent UA
2) Given your extensive use of headers and scripts, one would be inclined to believe that mass image grabs are avoidable
3) crawler or any variation of same has been a deniable criteria for UA's for at least fifteen years.
4) one of the first concerns for new webmasters is access to images by bots.
a) even the major search engines have proven records of 'hiccups', where their bots grabbed robots-denied-directories uncontrollably, and resulted in a practice of denials in place to prevent future 'hiccups'.
FWIW; the following are requests (robots.txt ONLY) from the wowrack Ip for Jan and thus-far-Feb 2018 and with the UA
"Mozilla/5.0 (compatible; DotBot/1.1; http:// www .opensiteexplorer .org/dotbot, firstname.lastname@example.org)"
(Note; spaces added in UA to break URL)
It's worth noting that DotBot is not contained in my robots, as a result I'm assuming that some other earlier name (unknown to me) results in their compliance.
7; two robots
14; two robots
15; six robots
16; two robots
17; one robots
18; three robots
19; four robots
22; two robots
26; one robots
29; one robots
19; one robots
[edited by: wilderness at 1:34 pm (utc) on Feb 21, 2018]