Within Reports, you can edit any report to customise to your liking. Press the Edit report button, then click the content tab.

Open the Reports window (menu: Tools -> Reports...) or the Report button on the button bar.
Select the report you like and want to modify.
Click the button "Edit Report" in the lower left of the Reports window.
You are now in the edit report window, which opens with three tabs: General, Content and Images.
Select the Content tab. You will now see the report layout in its parts.
Select the text field you want altered (like "DVDTitle1" or something alike).
In the left column, select "Font" and click on the ellipsis button (with the three periods ...).
Now the font window opens and you can select the Bold version of the font.
Exit by clicking OK and "Save&Close" etc. --- "cancel" will make you lose the change(s).

Note: changes are saved on your local PC. Be sure to backup or you may lose your changes if you migrate to your next PC whenever that happens in the future, or when you want to remove then reinstall the program.

If you're using the French translation of the application interface some button names can be different. Nevertheless I hope the above is sufficient.

One important thing first: Reports (rapports) refer to predefined lists which can be printed on paper on a printer, or a pdf, whatever you want. That was my understanding of the question.

If you mean a bold item in the collection list on screen:

The collections list (on the left side is usually the default view) can be modified extensively, but I am not sure in the default "list" mode. You may want to explore the various views of the collection list. Choose (menu) Collections -> View as list / View as details / View as thumbnails / Custom view... . The custom view can be edited to your liking very much but whether you can implement a rule like "bold" when it is a box set I am not sure.
Others here may be more proficient on this specific topic.

How to insert pictures:  How to do that is explained in the thread you yourself started in the "General Discussons" forum on this site.

Google translates now produces (with minor edits from me):
Une chose importante: Les rapports se réfèrent à des listes prédéfinies qui peuvent être imprimées sur papier sur une imprimante, ou un pdf, ce que vous voulez. C'était ma compréhension de la question.

Si vous voulez dire un élément en gras dans la liste de collection à l'écran:

La liste des collections (sur le côté gauche est généralement la vue par défaut) peut être considérablement modifiée, mais je ne suis pas sûr dans le mode "liste" par défaut. Vous pouvez explorer les différentes vues de la liste de collection. Choisissez (menu) Collections -> View as list / View as details / View as thumbnails / Custom view... (si en Anglais). La vue personnalisée peut être éditée à votre goût beaucoup mais si vous pouvez implémenter une règle comme "gras" quand c'est un ensemble de boîte je ne suis pas sûr.
D'autres ici peuvent être plus compétents sur ce sujet spécifique.

Comment insérer des images: Comment faire est expliqué dans le discussion vous avez vous-même commencé dans le forum "General Discussons" sur ce site.