Images usually contain metadata referred to as exif data. Nowadays this includes your camera or phone name and model. Also the location where the image was taken is also included if the GPS is enabled and you did not turn off geo-tagging.

Here’s how such exif data looks like (excluding location which I have disabled):

exiftool IMG_20171010_223446.jpg

ExifTool Version Number : 10.10
File Name : IMG_20171010_223446.jpg
Directory : .
File Size : 2.1 MB
File Modification Date/Time : 2017:11:14 20:26:18+01:00
File Access Date/Time : 2017:11:14 21:10:10+01:00
File Inode Change Date/Time : 2017:11:14 21:10:09+01:00
File Permissions : rw——-
File Type : JPEG
File Type Extension : jpg
MIME Type : image/jpeg
Exif Byte Order : Big-endian (Siemens, S)
Image Description : hdr
Make : NOKIA
Camera Model Name : NOKIA 1280 <<<<< what? It has not camer !
X Resolution : 72
Y Resolution : 72
Resolution Unit : inches
Modify Date : 2017:10:10 22:34:47
Y Cb Cr Positioning : Centered
Exposure Time : 1/20
F Number : 2.2
Exposure Program : Not Defined
ISO : 400
Exif Version : 0220
Date/Time Original : 2017:10:10 22:34:47
Create Date : 2017:10:10 22:34:47
Components Configuration : Y, Cb, Cr, –
Shutter Speed Value : 1/20
Aperture Value : 2.2
Brightness Value : 0
Exposure Compensation : 0
Metering Mode : Center-weighted average
Flash : Auto, Did not fire
Focal Length : 4.3 mm
Warning : [minor] Unrecognized MakerNotes
Sub Sec Time : 561680
Sub Sec Time Original : 561680
Sub Sec Time Digitized : 561680
Flashpix Version : 0100
Color Space : sRGB
Exif Image Width : 4032
Exif Image Height : 3016
Interoperability Index : R98 – DCF basic file (sRGB)
Interoperability Version : 0100
Sensing Method : One-chip color area
Scene Type : Directly photographed
Exposure Mode : Auto
White Balance : Auto
Focal Length In 35mm Format : 0 mm
Scene Capture Type : Standard
Device Setting Description : (Binary data 4 bytes, use -b option to extract)
GPS Latitude Ref : North
GPS Longitude Ref : East
GPS Altitude Ref : Above Sea Level
GPS Time Stamp : 20:34:46
GPS Processing Method : ASCII
GPS Date Stamp : 2017:10:10
Compression : JPEG (old-style)
Thumbnail Offset : 1298
Thumbnail Length : 5071
Image Width : 4032
Image Height : 3016
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
Aperture : 2.2
GPS Altitude : -2000 m Above Sea Level <<<< No I was not under water !!!
GPS Date/Time : 2017:10:10 20:34:46Z
GPS Latitude : 27 deg 45′ 14.1″ N
GPS Longitude : 43 deg 15′ 31.3″ W
GPS Position : 27 deg 45′ 14.1″ N, 43 deg 15′ 31.3″ W <<<<< and not not in the Atlantic ocean!!!
Image Size : 4032×3016
Megapixels : 12.2
Shutter Speed : 1/20
Create Date : 2017:10:10 22:34:47.561680
Date/Time Original : 2017:10:10 22:34:47.561680
Modify Date : 2017:10:10 22:34:47.561680
Thumbnail Image : (Binary data 5071 bytes, use -b option to extract)
Focal Length : 4.3 mm
Light Value : 4.6

To remove all exif data run the following:

exiftool -all= IMG_20171010_223446.jpg

The only remaining exif data will then be those that describe the properties of the image like its size and dimensions:

ExifTool Version Number : 10.10
File Name : IMG_20171010_223446.jpg
Directory : .
File Size : 2.1 MB
File Modification Date/Time : 2017:11:14 21:11:00+01:00
File Access Date/Time : 2017:11:14 21:11:03+01:00
File Inode Change Date/Time : 2017:11:14 21:11:00+01:00
File Permissions : rw——-
File Type : JPEG
File Type Extension : jpg
MIME Type : image/jpeg
Image Width : 4032
Image Height : 3016
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
Image Size : 4032×3016
Megapixels : 12.2