This issue touches upon two distinct GDPR rights:
Art 15 right to access: you have a right to receive a copy of all personal data concerning you that are undergoing processing (including storage). Access may only be denied where this would “adversely affect the rights and freedoms of others.”
Art 20 right to data portability: if processing is being carried out by automated means, and processing is based on certain legal bases (consent or contract, but not legitimate interest), then you have a right to receive a copy of your personal data in a machine-readable format, for personal data that you have provided to the data controller.
Whereas the right to access is fairly straightforward, the right to data portability applies under much more narrow conditions. Basically, it's a right that you can download any data that you've uploaded so that you can move to a different service.
Google Takeout is primarily concerned with your right to data portability, and provides your data in a machine-readable format. Any photos that you've uploaded to Google Photos, you'll be able to download. Thus, it could be technically compliant to exclude information that they've inferred about your personal data, such as image-recognition results.
Such results would still be personal data under the GDPR definition of the consent, and would be covered by your right to access. Google might argue that you already have access to this data through the web interface. In my opinion the GDPR clearly requires the data controller to provide a “copy”, i.e. the data in some durable form – not merely access through a web interface.
Whereas your question is specifically about Google, the same issue applies to other services as well. E.g. Ruben Verborgh has an interesting blog series on trying to get access to all their data from Facebook, though unsuccessful so far. Similar to your scenario, Facebook offers a download for personal data but does not include all personal data in this download. In one of the documents provided by Facebook in the course of the exchange, they note that they allow access to photo tags through the web interface, but do not include this in downloaded data – without providing further justification.