This can be achieved using
(?<=src=").*?(?=[\?"])
See working example on Regex101
Explanation
-
(?<=src=")
Prepended bysrc="
-
.*?
Lazy match any token -
(?=[\?"])
Until either a?
or"
would be the next token
If you might have a longer URL that doesn’t end with ?
(?<=src=").*?(?=[\*"])