Copy or symlink the slide files to the /usr/share/sddm/themes/breeze-slider2/CoverFlow/CoverImages/

Example:
sudo ln -s /image/files/source/*.* /usr/share/sddm/themes/breeze-slider2/CoverFlow/CoverImages/


[General]
---Standard Breeze---
type=color
color=black
background=
---Sliding cover---
coverColor=#80000000
coverWaitTime=180000
coverClock=components/StandardClock.qml
coverSuspenButton=system-suspend
coverRebootButton=system-reboot
coverShutdownButton=system-shutdown
coverSearchButton=system-search
---Extra background---
extraBackground=CoverFlow/main.qml
---CoverFlow---
CoverFlowFolder=CoverImages
AutoMoveInterval=2000
NumberOfCovers=5
CoverHeight=70
CoverMargin=10
BackgroundColor=#353535
CoverFlowBackgroundImage=
FillMode=
---Background Clocks----
backgroundClock=BackgroundClocks/FixedClock.qml
backgroundClockBackgroundColor=transparent
backgroundClockX=50
backgroundClockY=50
backgroundClockTimeFormat=HH:mm:ss
backgroundClockTimePointSize=32
backgroundClockTimeTextColor=white
backgroundClockDateFormat=dd-MM-yyyy
backgroundClockDatePointSize=18
backgroundClockDateTextColor=lightgray
