Retrieving a user's public google/gmail picture

I'm writing an email-based application using the gmail-api, and i need to retrieve user public images for email address originating from google. I've seen other applications do that, but i can't seem a way to reliably get this data.

some more information:

• i'm using oauth2 to sign the user in - and i have no problem requesting any type of permissions there.
• i've tried retrieving the image using the google+ api - but it requires a userID for that - and i don't know how to get the userId for the email address (gmail-api doesn't give it, afaik).
• i've tried using the contacts API - but it only gives images for the user's contacts, while the email clients can display images from other users as well.

Thanks!

Edit:

I know i can receive the required images from google plus, if i have the other user's userid. however, i can't find a way to get the userid based on an email address.

Is very easy

http://picasaweb.google.com/data/entry/api/user/<hereYourUserIdOrYourEmail>?alt=json

just has a little problem.

You only can get the picture of your Google+ profile, not directly from your gmail.

UPDATE:

This API is being deprecated and will be turned down in January 2019. Migrate to Google Photos Library API as soon as possible to avoid disruptions to your application.

More Info Here

UPDATE:

This API is being deprecated and will be turned down in January 2019. Migrate to Google Photos Library API as soon as possible to avoid disruptions to your application.

Info Here

Based on @jose920405 answer, I have written this free public API service called Pikmail API. Here some advantages.

• No authentication needed.
• It's totally free and open source.
• It's written in Kotlin.
• You don't need to write some wrapper for mapping the response.

Here is the blog post about how Pikmail API works internally.

Usage:

Html

<img src="https://pikmail.herokuapp.com/[email protected]?size=50" alt="Profile Picture">

Java Android

Picasso.with(context).load("https://pikmail.herokuapp.com/[email protected]?size=50").into(imageView);

Feel free to contribute with you pull requests, open bugs or request new features here.

Note: This service is based on an independent library called Pikmail that can be used as a Gradle dependency in your java projects(servers or Android apps).

Google+ is the right way to do this. This actually has nothing to do with the Gmail API. You don't need a the user's userid, just a valid access token with appropriate scopes.

https://www.googleapis.com/plus/v1/people/me?access_token=YOUR_ACCESS_TOKEN_HERE

Unless there is an error/invalid token/etc, this will return a bunch of information about the user as JSON. Included in this data will be a URI for the user's profile image.

EDIT:

To get the profile picture for a user based on the email address, first search for the user

https://www.google.com/m8/feeds/contacts/default/thin?q=EMAIL_ADDRESS_HERE

You can then retrieve the correct userID for that user from the returned JSON, and use it to get a profile image.

If you are authenticating users in your app with Google using the OAuth 2.0 API -For example using passport -> https://www.npmjs.com/package/passport-google-oauth20

You can request the "profile" scope, which gives you a bunch of information from displayName to the users profile photos "profile.photos[0]"