A CSV file can only contain text. So you'll need to ensure all product images are on an existing website. Those image URLs will only be used during the CSV importing process (in other words, you can delete them when your import is done).
If the files are on your computer only,
You can upload them in bulk to the Site >Files section of your StoreHippo Admin Panel. Please refer to Files for more details. Once uploaded to files section you can use the relative path of the file. For example: abc.jpg, folder1/abc.jpg etc or use the full URL of the uploaded image file.
You can also upload the files to another image hosting service like Dropbox, Google drive etc and use the link to the image URLs in CSV.
If you are switching to StoreHippo from another platform, you're all set. Just copy the current image URLs and use them in the CSV file.
If the product CSV file was produced by exporting your products from StoreHippo then you don't need to do anything since your images are already on your website.