I tested uploading the same image for multiple service items and confirmed that there is no limit on using it, admin.
Here's the sample screenshot below:

Since you're unable to upload the image, let's clear your browser cache, as this can affect the performance of uploading it in QuickBooks Online. You can also utilize other supported browsers to see if your current one is incompatible with QuickBooks.
If you want to track the value of your inventory assets manually, you can check this article as a future guideline: Track inventory manually in QuickBooks Online.
If you need further assistance, feel free to comment below.