Non-Capturing Group(?:\G(?!\A)|<img) \Gstart of current search
<imgthe literal text <img (case sensitive) Group with flags gxs(?s:.+?\bsrc=['"]) s modifier: single line. Allows a dot to match line terminators
.+?any character, repeated at least once
\ban ASCII word boundary
src=the literal text src= (case sensitive) 'the literal ' (3910 / 478 / 2716)
"the literal " (3410 / 428 / 2216)
\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
httpthe literal text http (case sensitive) s?optionally matches the literal s (11510 / 1638 / 7316) (case sensitive)
.+?any character (except for line terminators), repeated at least once
Positive Lookahead(?=/wp-content/) /wp-content/the literal text /wp-content/ (case sensitive) g modifier: global. Finds all matches instead of stopping after the first
x modifier: extended. Ignores unescaped whitespace and comments outside character classes