You can make the system ignore some assets in 1 of 2 ways.
In both cases, keep in mind that the target must be the tag containing your asset's URL so, for instance, a <img> tag with an src, or a <script> or <style> tag.
If you're targetting a <picture> tag and want to manually add the data-ignore attribute to it you must add it to each <source> and <img> tags nested inside your <picture> tag that you want to ignore.
In the same way, if you want to exclude it through the Blacklist setting, your REGEX pattern must target the resource's URL. So, for instance, the image's URL or the script's URL.