The "GD Library" is the most used image-processing tool in PHP, allowing the dynamic creation and editing of images, charts, thumbnails, etc.

The file types that can be created and/or edited using the GD library are GIF, JPEG and PNG.

The GD library will be included with most PHP installations. To confirm if the GD library is activated on your server/host, you can run <?php echo phpinfo(); ?> and scroll down to "GD" to confirm its status.

The GD library includes over 100 functions:

Function	Description
gd_info	Retrieve information about the currently installed GD library
getimagesize	Get the size of an image
image_type_to_extension	Get file extension for image type
image_type_to_mime_type	Get Mime-Type for image-type returned by getimagesize, exif_read_data, exif_thumbnail, exif_imagetype
image2wbmp	Output image to browser or file
imagealphablending	Set the blending mode for an image
imageantialias	Should antialias functions be used or not
imagearc	Draws an arc
imagechar	Draw a character horizontally
imagecharup	Draw a character vertically
imagecolorallocate	Allocate a color for an image
imagecolorallocatealpha	Allocate a color for an image
imagecolorat	Get the index of the color of a pixel
imagecolorclosest	Get the index of the closest color to the specified color
imagecolorclosestalpha	Get the index of the closest color to the specified color + alpha
imagecolorclosesthwb	Get the index of the color which has the hue, white and blackness
imagecolordeallocate	De-allocate a color for an image
imagecolorexact	Get the index of the specified color
imagecolorexactalpha	Get the index of the specified color + alpha
imagecolormatch	Makes the colors of the palette version of an image more closely match the true color version
imagecolorresolve	Get the index of the specified color or its closest possible alternative
imagecolorresolvealpha	Get the index of the specified color + alpha or its closest possible alternative
imagecolorset	Set the color for the specified palette index
imagecolorsforindex	Get the colors for an index
imagecolorstotal	Find out the number of colors in an image's palette
imagecolortransparent	Define a color as transparent
imageconvolution	Apply a 3x3 convolution matrix, using coefficient and offset
imagecopy	Copy part of an image
imagecopymerge	Copy and merge part of an image
imagecopymergegray	Copy and merge part of an image with gray scale
imagecopyresampled	Copy and resize part of an image with resampling
imagecopyresized	Copy and resize part of an image
imagecreate	Create a new palette based image
imagecreatefromgd2	Create a new image from GD2 file or URL
imagecreatefromgd2part	Create a new image from a given part of GD2 file or URL
imagecreatefromgd	Create a new image from GD file or URL
imagecreatefromgif	Create a new image from file or URL
imagecreatefromjpeg	Create a new image from file or URL
imagecreatefrompng	Create a new image from file or URL
imagecreatefromstring	Create a new image from the image stream in the string
imagecreatefromwbmp	Create a new image from file or URL
imagecreatefromxbm	Create a new image from file or URL
imagecreatefromxpm	Create a new image from file or URL
imagecreatetruecolor	Create a new true color image
imagedashedline	Draw a dashed line
imagedestroy	Destroy an image
imageellipse	Draw an ellipse
imagefill	Flood fill
imagefilledarc	Draw a partial arc and fill it
imagefilledellipse	Draw a filled ellipse
imagefilledpolygon	Draw a filled polygon
imagefilledrectangle	Draw a filled rectangle
imagefilltoborder	Flood fill to specific color
imagefilter	Applies a filter to an image
imagefontheight	Get font height
imagefontwidth	Get font width
imageftbbox	Give the bounding box of a text using fonts via freetype2
imagefttext	Write text to the image using fonts using FreeType 2
imagegammacorrect	Apply a gamma correction to a GD image
imagegd2	Output GD2 image to browser or file
imagegd	Output GD image to browser or file
imagegif	Output image to browser or file
imagegrabscreen	Captures the whole screen
imagegrabwindow	Captures a window
imageinterlace	Enable or disable interlace
imageistruecolor	Finds whether an image is a truecolor image
imagejpeg	Output image to browser or file
imagelayereffect	Set the alpha blending flag to use the bundled libgd layering effects
imageline	Draw a line
imageloadfont	Load a new font
imagepalettecopy	Copy the palette from one image to another
imagepng	Output a PNG image to either the browser or a file
imagepolygon	Draws a polygon
imagepsbbox	Give the bounding box of a text rectangle using PostScript Type1 fonts
imagepsencodefont	Change the character encoding vector of a font
imagepsextendfont	Extend or condense a font
imagepsfreefont	Free memory used by a PostScript Type 1 font
imagepsloadfont	Load a PostScript Type 1 font from file
imagepsslantfont	Slant a font
imagepstext	Draws a text over an image using PostScript Type1 fonts
imagerectangle	Draw a rectangle
imagerotate	Rotate an image with a given angle
imagesavealpha	Set the flag to save full alpha channel information (as opposed to single-color transparency) when saving PNG images
imagesetbrush	Set the brush image for line drawing
imagesetpixel	Set a single pixel
imagesetstyle	Set the style for line drawing
imagesetthickness	Set the thickness for line drawing
imagesettile	Set the tile image for filling
imagestring	Draw a string horizontally
imagestringup	Draw a string vertically
imagesx	Get image width
imagesy	Get image height
imagetruecolortopalette	Convert a true color image to a palette image
imagettfbbox	Give the bounding box of a text using TrueType fonts
imagettftext	Write text to the image using TrueType fonts
imagetypes	Return the image types supported by this PHP build
imagewbmp	Output image to browser or file
imagexbm	Output XBM image to browser or file
iptcembed	Embeds binary IPTC data into a JPEG image
iptcparse	Parse a binary IPTC block into single tags.
jpeg2wbmp	Convert JPEG image file to WBMP image file
png2wbmp	Convert PNG image file to WBMP image file

We will learn about some of the more interesting functions over the course of the next few pages.