How to get information about an image (picture) from the Linux command-line?

For some image formats you can just use the file command:

$ file MyPNG.png 
MyPNG.png: PNG image, 681 x 345, 8-bit/color RGB, non-interlaced

Not all image formats report the size (JPEG most notably doesn't):

$ file MyJpeg.jpg 
MyJpeg.jpg: JPEG image data, JFIF standard 1.01

For those you will have to use something more elaborate, like:

$ convert MyJpeg.jpg -print "Size: %wx%h\n" /dev/null
Size: 380x380

The convert command is part of the ImageMagick package.

The best way to get this information is by using the identify command:

$ identify image.png

or only size atributes

$ identify -format "%wx%h" photo.jpg

It is part of ImageMagick, which you can install on Ubuntu like so:

$ sudo apt-get install imagemagick

exiv2 is "the tool" to get information from picture files:

~$exiv2 myimage.jpg

outputs:

File name       : myimage.jpg
File size       : 1196944 Bytes
MIME type       : image/jpeg
Image size      : 2592 x 1944
Camera make     : LG Electronics
Camera model    : LG-P970
Image timestamp : 2013:05:19 17:27:06
Image number    : 
Exposure time   : 1/9 s
Aperture        : 
Exposure bias   : 0 EV
Flash           : Yes, compulsory
Flash bias      : 
Focal length    : 3.7 mm
Subject distance: 
ISO speed       : 745
Exposure mode   : 
Metering mode   : Average
Macro mode      : 
Image quality   : 
Exif Resolution : 
White balance   : Auto
Thumbnail       : image/jpeg, 13776 Bytes
Copyright       : 
Exif comment    :