The defined keyboard shortcuts are not configured to work during Playback mode. To make them work, you have to customize the shortcuts.
Quit MC, and go to the folder C:\Program Files (x86)\J River\Media Center 19\Data. Create a new folder:
C:\Program Files (x86)\J River\Media Center 19\Data\Custom Resources
and add a new text file named Resource.xml, and add the contents below to that file. Then open MC and your ratings should now work during Image playback.
<!--
Media Center Resource XML (Custom / English)
-->
<MJRS version="1.0">
<!--
ACCELERATORS:
Key: semi-colon delimited list of key strokes to be pressed (see list below for special keys)
note that the only valid combinations are: [Key], [Key];Ctrl, [Key];Ctrl;Shift, [Key];Alt
Type: the type of command (defaults to MCC)
MCC: the command is an MC command
Program: the command is a program to run
Command: the MCC command index / name of program
Param: the parameter for the MCC command / program arguments
TranslateFlags: flags that determine when and how an accelerator is translated (binary or'd together)
1: don't translate in edits, comboboxes, and other data entry controls
2: don't translate in fullscreen mode or theater view
4: don't translate in any type of popup window
8: only translate in fullscreen
16: don't translate in IE, VB controls, or other unknown rich controls
32: targets playback engine / display (DVD, image playback, etc.)
64: only translate when Action Window is focused
NoShowAsShortcut: 1 if you don't want MC to show this shortcut in menus, tooltips, etc.
Global: 1 if you want the accelerator to be translated even when MC doesn't have the focus
Special key list: Insert, Delete, -, +, Right, Left, Up, Down,
NumPad0, NumPad1, NumPad2 (etc.), F1, F2, F3 (etc.), Backspace, Enter, Escape,
Apps, Page Up, Page Down, Home, End, Space, Print Screen, Tab
Remember that order is relevant when the same shortcut appears multiple times.
-->
<ACCELERATORS>
<!-- Rate current song -->
<Entry Key="Ctrl;Shift;0" Command="10023" Param="0" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;1" Command="10023" Param="1" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;2" Command="10023" Param="2" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;3" Command="10023" Param="3" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;4" Command="10023" Param="4" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;5" Command="10023" Param="5" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;NumPad0" Command="10023" Param="0" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;NumPad1" Command="10023" Param="1" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;NumPad2" Command="10023" Param="2" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;NumPad3" Command="10023" Param="3" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;NumPad4" Command="10023" Param="4" TranslateFlags="32" />
<Entry Key="Ctrl;Shift;NumPad5" Command="10023" Param="5" TranslateFlags="32" />
</ACCELERATORS>
</MJRS>