I presume you have canned routines that can do that for you, routines for which you can provide some control by varying numerical parameters, or twisting GUI buttons and sliders that vary those parameters for you.

But you apparently do not have the ability to operate down at the pixel level for direct manipulations, like making filters, convolutions and resamplings. (I want to insert THIS value directly into THAT pixel.)

For example, if Kirktrump is an image of L lines and S samples, where any one pixel can be identified as Kirktrump (LINE, SAMPLE), the mirror reflection Trumpkirk can be created by the following pseudocode:

DO LINE = 1,L
DO SAMPLE = 1,S

FROMPIXL = S - SAMPLE + 1
Trumpkirk (LINE,SAMPLE) = Kirktrump (LINE, FROMPIXL)

ENDDO

The variable duple (LINE,FROMPIXL) is the sample location in the input image from where the pixel is copied for insertion into the location (LINE,SAMPLE) in the output image. Since this algorithm describes a "mirror" effect, the sample locations in each line are swapped, but the line numbers are not. If you swap lines AND samples its called a "flip".