A properly formed URL can instruct Piwigo to generate a re-sized image. The structure is as follows:

piwigo/i.php?/galleries/{path to album}/{image file name}-{size code}.jpg

Size codes are as follows:

Size code Resulting size
2s extra extra small xxs
xs extra small xs
sm small s
me medium m
la large l
xl extra large xl
xx extra extra large xxl
Special sizes
th thumbnail
sq square

Example to generate an extra extra small image: