I'm sorry. Unfortunately, in order to attach / post data files, such as documents or photos, on any website or on any third-party email service (not Gmail), then you would need to have a local copy of your data on your computer's local hard drive.
- The reason you are able to access your google drive using that service is because you have the Google Drive data files saved (synced) on your computer's hard drive, not just online. Therefore, Google Drive data is taking up storage space on your computer's hard drive, whereas Google Photos is not.
- So if you want to attach Google photos to that service, then you would need to have a copy of those photos on your computer's hard drive, i.e., you would need to download the photos (that you want to attach) to the computer first, then attach, then you can delete the downloaded photos.
- Basically, you cannot access online data from Google (Drive or Photos) from a third-party service. You have to have local copy, or you have to download / save to the computer first, then attach / upload.
- Note: There are some third-party services that lets you access online data directly, such as Yahoo Mail lets you access / attach data directly from Google Drive and Dropbox even if you do not have Google Drive or Dropbox installed on your computer / even if you do not have a copy of the Google Drive data or Dropbox data on your computer's hard drive. Only if a third-party has that feature, then you can access Google online data directly.
Please let me know if this is not clear. Thank you.