Hi,
Please note that after uploading the images, they are being created in the three folders:
wp-content/uploads/photo-gallery– images with modified dimensions,
wp-content/uploads/photo-gallery/.original– the original image and
wp-content/uploads/photo-gallery/thumb– images with Thumbnail dimensions.
There is also a separate folder for images uploaded from the Media Library in the Uploads folder. It works same as it is in the above described.
You can access via FTP and try to delete the images from these folders.
Please let us know if you have further questions.
Thank you! Have a nice day!`