SUMMARY
KTimeTracker uses custom icons from its source code repository ( https://cgit.kde.org/ktimetracker.git/ ). Most of them are raster and too small for modern screens. And none of them match Breeze style. It would be nice to release KTimeTracker 5.0 with modern icons/artwork.

I will list and describe each of the icons:

1. pics/active-icon.gif. It used to be 8 raster images, I merged them into this GIF. This is used as tray icon when a task is active (i.e. time tracking is ON at the moment).

When no tasks are active, a fixed frame of this GIF is used as tray icon.

Drawbacks:
 - Raster image, should be an SVG
 - The colors do not match modern icon themes, should be a Breeze icon
 - Animated. In my opinion, constantly running animation might distract users. However I have no good ideas on how to tell the user that a task is active without using animation, may be add a red dot on top of normal icon - the one that is commonly understood as "recording"/LIVE.
 - The current animation has low FPS (1 FPS), thus I need to look at the tray icon for a whole second just to check if . If we choose to continue using animation, it should be made smooth, I can for example animate a clock face overlay programmatically at a higher FPS.

2. pics/watch.gif. Used in list view the the application window when a task is active. It's mostly good, but is a raster one as well, might look pixelated on high resolution screens. Low FPS of animation is not that big of a problem here because if you need an icon is list view, then the respective task is obviously active (otherwise the watch.gif icon is hidden).

3. empty-watch.xpm. Just an empty image. Placeholder for when watch.gif is not used in the list view.

4. task-incomplete.xpm, task-complete.xpm. Has two uses:
 - Icons for actions "Mark as Complete" / "Mark as Incomplete"
 - Task completion indicator in the list view. If progress of a task is at 100%, then "task-complete" is used. Otherwise, "task-incomplete" is used. The indicator is clickable: it toggles task completion (sets task progress to 100% or to 0%, depending on the previous state).

Both of these are raster images and do not match the Breeze icon theme, this is not good for display in menu items and/or on toolbar.

May be the task completion indicator in list view should use a different icons, they don't have to be the same with the action items. And we probably don't really need that clickable behaviour of the indicator, it's a quite obscure and hacky feature anyway, may be at least replace it with a regular checkbox.

5. icons/*-actions-subtask-new-ktimetracker. This icon does not match Breeze theme.

It is used for the "Add Subtask..." action. A similar action "Add Task" (adds top-level task) uses the standard icon "document-new" which is already present in Breeze themes.

6. icons/*-apps-ktimetracker. Application icon.

Looks good to me, however you might say it looks old.