What is com.sec.android.gallery3d?
The Android operating system on a mobile phone includes various cache directories and files that are designed to store data for future use so that when a file is reopened it can be loaded more quickly.

This can cause storage space issues as most user data is not only stored within the handset as chosen by the user, the operating system it is also stored as a backup within other hidden system files, effectively meaning that the files are doubled up on a device including within a file name com.sec.android.gallery3d.
Stored Images within com.sec.android.gallery3d
For example, an image is captured using the device. It is automatically stored to the DCIM folder on an Android phone.
In order to access that image within the DCIM folder, the Gallery application is used to browse them.
This application is available on Android phones by default and allows the user to scroll through the content of the DCIM folder with the images present being displayed as a smaller thumbnail type image.
The application allows the user to view the content of each of the images within the DCIM folder, those stored to the handset, without the need to open each of the images individually.
Those smaller thumbnail versions of the images displayed to the user whilst they scroll through the content of the DCIM folder using the Gallery application are retained by the Android operating system so that, if the user decides to do the same thing again tomorrow and scroll through the images on the handset, the smaller images that are displayed will not have to be created again, meaning that the phone has to do less to show them.
Importance of com.sec.android.gallery3d in Mobile Phone Forensics

The result of this activity is that those small images are stored to the handset within a file named com.sec.android.gallery3d in the data directory on the device.
Whilst storing an image within that file in this way is not a significant issue, when the user may have hundreds of images stored to their phone, that com.sec.android.gallery3d file becomes large in size and occupies a high proportion of the storage space of the handset.
In addition to this, even when the original version of the image is deleted, the copy of it within the com.sec.android.gallery3d remains.
The user also cannot normally see or access the com.sec.android.gallery3d file, making it useful to consider as part of a mobile phone forensic investigation, as it often contains files that were stored to the device previously. Potentially allowing for the identification of images believed to have been deleted from the phone by the user
It is possible for the user to manually delete the com.sec.android.gallery3d file within the data directory using a file manager application, which would remove the images within the cache at that point, any further access of the Gallery application would regenerate new versions of the images within the cache file com.sec.android.gallery3d.
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