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There are a few things you should know.
First, Excel inserts pictures on their own display layer which is superimposed over the worksheet grid. Any picture or other shape on the graphics layer can be moved to any position on the screen, relative to or independent from the underlying worksheet.
Second, pictures are loaded either by reference or by value (in fact, I am not sure right now if the latter is supported by Excel). "ByRef" means that the workbook only contains the picture's file name (including full path). When the workbook is opened the picture is loaded and displayed but if you copy the workbook to another computer the picture can't be shown because it isn't available at the address saved in the workbook. If you need the picture to be available wherever the workbook is then the picture must be fully embedded in the workbook itself.
Third, pictures are very voluminous. A single picture would be several times the size of your workbook. This affects the time it takes to save a workbook and the time it takes to print.
Fourth, if you have linked pictures in your workbook - perhaps many pictures - and you have enabled "update links on Open" and/or "update links before Print" and/or "update links before Save" all pictures files linked to the workbook will be opened one by one, updated and closed again. This will take time.
Therefore the solution to your problem must be looked for in the settings you use while importing pictures as well as the settings for the Excel application as a whole.