To upload images to Shopify line-item – there are two ways. First: you can install and subscribe to image uploader app, which will same time and get you started quickly – should cost approximately $10/month. Second: you can hire a Shopify developer to customize your existing theme to upload images to Shopify cart line-item via product page.
Thirdly: you can google “how to upload images to Shopify line-item via product page and most probably – you’ll get a good helpful tutorial to follow steps tp make the changes on your product template to upload image to Shopify line-item.
Shopify Image Uploader Apps
Here is a list of most popular image uploader Shopify apps that come ready-made options but still you might have a unique idea that might not fit within the options of these apps, in that case – you should hire a Shopify developer or look up for tutorials.
These will approximately cost you $10 but most of them have trial too.
Shopify Image Upload Demo Video
This video show both the options – first – without using image uploader app and second – using the app.