Sending pictures via http with an ESP32-CAM

Pictures taken with the ESP32-CAM can be sent in a multipart/form-data type content via HTTP. Here is a sample code to achieve this:

#define BOUNDARY     "--------------------------133747188241686651551404"  
#define API_ROUTE "/upload"
#define API_HOST "192.168.1.2"
#define API_PORT 80

void upload_image(){

  // Get a frame
  camera_fb_t * fb = NULL;
  fb = esp_camera_fb_get();
  
  if (fb) {
    // Frame was taken successfully, now sending it

    // Define the client that will be used for the API call
    WiFiClient client;

    // Attempt a connection
    if (client.connect(API_HOST, API_PORT)) {

      // Connection was successful, prepare the request content
      String body_pre_image;
      body_pre_image = "--";
      body_pre_image += BOUNDARY;
      body_pre_image += "\r\n";
      body_pre_image += "Content-Disposition: form-data; name=\"imageFile\"; filename=\"picture.jpg\"\r\n");
      body_pre_image += "Content-Type: image/jpeg\r\n";
      body_pre_image += "\r\n";
    
      String body_post_image = String("\r\n--")+BOUNDARY+String("--\r\n");
    
      int total_length = body_pre_image.length()+body_post_image.length()+fb->len;
      
      String header_text;
      header_text =  "POST " + String(API_ROUTE) + " HTTP/1.1\r\n"; // the method is defined here
      header_text += "cache-control: no-cache\r\n";
      header_text += "Content-Type: multipart/form-data; boundary=";
      header_text += BOUNDARY;
      header_text += "\r\n";
      header_text += "content-length: ";
      header_text += String(total_length);
      header_text += "\r\n";
      header_text += "\r\n";
   
      // Now send the whole thing
      client.print(header_text+body_pre_image);
      client.write(fb->buf, fb->len);
      client.print(body_post_image);
      
      // timeout management
      unsigned long timeout = millis();
      while (client.available() == 0) {
        if (millis() - timeout > 5000) {
          Serial.println("Timeout");
          client.stop();
          break;
        }
      }
    }

    // No matter the result of the upload, clean up the frame buffer
    esp_camera_fb_return(fb);
    fb = NULL;
    
  }
 
}