In C# you can use following code:
string html = @"
<h1>
<img src="" ... >
</img>
<img></img>-bad
<img/>-bad
<img src="" ... />
</h1>";
string result = Regex.Replace(html, @"<imgs[^>]*>(?:s*?</img>)?", "", RegexOptions.IgnoreCase);
But be aware that modifying HTML with Regex isn't good approach, its better to use Html Agility Pack
or other HTML parsers.
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