As soon as I add pictures to my project, such as full size background, Captivate is very slow. Is there a way to compress the size of the pictures while already added to the project in Adobe Captivate? Or do I have to do that before using them in my project, in Photoshop for example?
If you're dumping full high-resolution images straight onto Captivate slides then you are bloating your project filesize and potentially weighing down the download required to view the final content.
Resize your images in Photoshop (as you suggested) or some other graphics editor BEFORE importing them into Captivate. Just work out what their final size in the output needs to be and reduce them to that size before import.