Compare methods of sending photos to server

In a mobile app where users can create announcements and upload one or many photos, the choice of the approach for sending photos will impact performance. So comparing methods in terms of performance and consider their scalability when dealing with a large number of users Can be challenging. That's why i'm asking this question. 3 methods have been chosen:

1. Sending photos One by One (Sequentially)
2. Sending photos One by One (Parallel requests)
3. Sending photos in One endpoint (batch upload)

Any help would be appreciated. It will be great if any ressources or articles were provided or answers were supported by articles.

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