This would be simple and easy to batch convert your photo, please goto Irfanview download the latest version:

Step 1:  Open IrfanView > Batch Conversion/Rename


Step 2:

  1. Right side select your photo and add in the batch
  2. Output directory for result files, please select which folder for the conversion output
  3. Select “Output format” and click “Options”

Step 3: JPEG select the Save quality, 100% is original size, here default resize is 80%


Step 4. Click “Start Batch” and wait it finish


Result :

Left is original size 905MB after reducing to 80% the size is 234MB, please check and make sure the quality is suitable for flushing photos and you accept before delete the original photo.