You can use a regular expression.
Try
Dim RegexObj As New Regex("<img[^>]+src=[""']([^""']+)[""']", RegexOptions.Singleline Or RegexOptions.IgnoreCase)
Dim MatchResults As Match = RegexObj.Match(SubjectString)
While MatchResults.Success
' SRC attribute is in MatchResults.Groups(1).Value
MatchResults = MatchResults.NextMatch()
End While
Catch ex As ArgumentException
'Syntax error in the regular expression (which there isn't)
End Try
Here's how it works:
<img[^>]+src=["']([^"']+)["']
Match the characters "<img" literally «<img»
Match any character that is not a ">" «[^>]+»
Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Match the characters "src=" literally «src=»
Match a single character present in the list ""'" «["']»
Match the regular expression below and capture its match into backreference number 1 «([^"']+)»
Match a single character NOT present in the list ""'" «[^"']+»
Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Match a single character present in the list ""'" «["']»