Photos in the Camera folder in the Gallery were deleted automatically in my Android phone
In the comments you said: 


  I have found many previously sent images in WhatsApp now which confirms that images has not been deleted. But the matter is that the images are not shown in the gallery. What should I do to recover image?


So you are telling me that the images are still on your phone, but not deleted? If that is the case it may be cause of a .nomedia file in the same folder as your photos.  

You should check in your whatsapp folder and look for a .nomedia file. (/Whatsapp/).
And for your photos you made with the camera app, you should look in /DCIM/Camera/ (you can do that e.g. using the "My Files" app which is pre-installed on your device; the .nomedia files could be in DCIM or in DCIM/Camera – ignore other locations for now). 
If you find a .nomedia file in one of these directories, then you should delete the file and then your photos should appear again in your gallery. If you still don't see the photos after you deleted the file, reboot your phone.

Hope my answer helps! If there is no .nomedia file, leave a comment below so I can help you further.