slice (3rd left)
File > Export > Save for Web (legacy)

:: important
File > New > Document Type (Web)
View > Rulers
Window > Info (change to pixels)

:: guides
view > new guides (to key in position)
view > new guide layout (change preset to create quickly)

Change canvas color
choose foreground color, use paint bucket tool (under gradient)

create a blank layer below, add marqee (paint bucket with color)
select photo, right click, create clipping mask

select 2 vector shapes
layer > combine shape > subtract front shape

horizontal guides:
15, 22, 40, 64, 80, 220, 235, 315, 330, 345, 635, 650, 652, 666, 681, 698

vertical guides:
40, 120, 140, 220, 240, 320, 340, 420, 450, 505, 660, 740, 760, 840, 860, 940