I don't think there is anything better than Excel for totalling a list of values.

Also your concern "I would also prefer to embed the images in the spreadsheet rather than linking to external files in order to reduce the risk of images going astray." is worrying too much unless you are an anxious person.

If you are a disciplined person then I suggest using links and all you have to do to "stop images going astray" is to ensure all photos are in a single dedicated folder and do not ever delete it, rename it (or the photos it contains), or move it or else the links won't work anymore. To help you to adhere to this rule you could name the folder with a warning in the folder name. e.g. "Insurance photos - Do NOT Delete".

Good luck.