That’s a very bad example from Google:
- The
alt
content "logo" is usually not appropriate for a logo (unless the company/etc. is named "logo"). - An
img
with Microdata’sitemprop
attribute still needs analt
attribute.
There are no conflicts between alt
and itemprop
. Your example with both of these attributes is fine.
To describe your logo in greater detail, you would need to find an appropriate Microdata vocabulary. If you want to use the schema.org vocabulary, the type ImageObject
is probably the best you can get currently.
You could also use the longdesc
attribute (currently a Working Draft) "to link descriptions to images in HTML5 content".