I made a 3x3 grid of these images and added strokes to them using the "Objects to Pattern" option. Since I need to print it and then cut it, I wanted to mark only the corners.
Summarizing, I want to know if there is a way to make this:
Become this:
I tried to use the "Markers" option in the "Stroke Style" tab but it only marked the top-left corners, is there a way to mark all 4 corners without needing to do it manually?
transformed the bitmap image to a pattern (select image > Object > Pattern > Object to pattern)
designed a small red cross and transformed it to marker (Object > Object to marker)
then you're nearly there : you did open fill an stroke dialog to use the red cross marker as Start Marker, just enable the Mid Markers and choose Fixed specified angle option as shown on screenshot.
When creating your clone tiling with clone > create tiled clones, don't forget to open inkscape preferences dialog and browse to tools and enable geometric bounding box, or marker's size will make issues, or use LPE tiling.
I made a 3x3 grid of these images and added strokes to them using the "Objects to Pattern" option. Since I need to print it and then cut it, I wanted to mark only the corners.

Summarizing, I want to know if there is a way to make this:
Become this:
I tried to use the "Markers" option in the "Stroke Style" tab but it only marked the top-left corners, is there a way to mark all 4 corners without needing to do it manually?
I understand that you
then you're nearly there : you did open fill an stroke dialog to use the red cross marker as Start Marker, just enable the Mid Markers and choose Fixed specified angle option as shown on screenshot.
When creating your clone tiling with clone > create tiled clones, don't forget to open inkscape preferences dialog and browse to tools and enable geometric bounding box, or marker's size will make issues, or use LPE tiling.