This issue is really one of practicality and can be especially important if there is significant archive content or unskilled users will be managing the site.
- Would it be impractical to update existing
- Do the content producers have the technical ability to implement and maintain specific markup?
- Is extra markup okay if the technique or site design is changed in the future?
- What are the accessibility implications?
Most techniques for implementing responsive images utilse some kind of specific markup
in or around each image tag. This can be anything from additional attributes on the
tag itself to completely custom and non-standard markup which only uses an
tag as a fallback.
Relying on specific markup can be problematic for a variety of reasons.
If there is a large amount of legacy content, going back and implementing the new responsive technique around all images may be a non-trivial exercise. Even if there is a large amount of legacy content, it may not be important that it gets updated. Maybe the majority of visitors to the site only see content and ignoring archived content is a compromise worth making.
Another important consideration is future content. Many sites are managed by non-technical users and ensuring that each image tag has the required specific markup might not be possible. Maybe the site's CMS has a WYSIWYG editor which authors use to insert images; can it be adapted to ensure that every image is inserted with the required markup?
If the site's design is updated in the future, will the additional markup for each image be problematic?