Question: As stated in [Dropbox FAQ](https://www.dropbox.com/help/288/en):

> 
> Camera Upload tries to be smart about not uploading the same photos
>  and videos more than once. It will not re-upload these files even if
>  you move, rename, or delete them from the Camera Uploads folder.
> 
> 
> 

So, how can I clear this "cache" and reupload all photos again after deletion?

Answer: 
I'm using the android app and I just go to the "Camera Uploads" folder and select "Upload here" from the menu. 

You then get asked to select "Photos and videos" or "Other files". Select "Photos and videos".

Choose the photo you want to upload and select Upload.

If the file exists, it will ask if you want to replace the file.
Try to delete the photos from the trash bin after deleting them from your photo uploads folder and, after this, re-upload the photos. 

If still not possible, use a different file name and when it's about hundreds of photos use something like a "bulk rename utility."