Slicing by guidelines actually on an image

[Redraw]

I hope I'm on the same idea, I could be wrong so my attempt

You got the image open use the free select tool (F)
started near a corner left click > press select on keyboard (Keep pressing) move mouse to locations still pressing select button move and click mouse until you finish back near starting point

you now will have the making of a grid over the image

> release select button mouse click on yellow dot to finish loop
> right click use 3rd option down > select > to path
> open path dialog tooltab > right click on the path you made use the stroke path option

>options chosen Capimage_0233.png
edit later
> stroke with the paint tool left click stroke
> sounds obvious but remember to use a contrasting color (heh heh that's I will tell you)
>ctrl+shift+A = removes the path guide lines
> drop down and across the guide lines for slicing > sliced and done

> Capimage_1000.png
edit  will later have links
With the screenshot images could not post was going to go to something like ImageBam  or similar  next year might have to go there today.

I hope this helps you.
 Noel