Border Size Color
border
Draws a border around the image, in the width and color defined. The border will overlap the image rather than altering its size.
The default is no border, and the width and color values must be specified as a comma-separated list with the width first. Valid color values are a color keyword or 3- (RGB), 4- (ARGB) 6- (RRGGBB) or 8-digit (AARRGGBB) hexadecimal values. The “A” in a 4- or 8-digit hex value represents the color’s alpha transparency. The default is transparent white, 0FFF.
To round the corners on a bordered image, use the border-radius and border-radius-inner parameters in addition to border.
There are four additional parameters for adjusting the border size on individual sides of an image. The border parameter must be set for these additional parameters to take effect.
Documentation for these parameters can be found in the links below: