Here are some product ideas I generated using Midjourney. All mockup photos are generated in Artboard Studio. I've included the Midjourney prompts as the image captions.
When creating sticker designs, use words like die-cut, sticker design, white background in your prompt. I've tested a few version, and found that sometimes version 4 generates better results than version 5 of Midjourney.
Then use tools like https://www.remove.bg/ or one of the other tools mentioned in the previous chapter to remove the background.
Repeating patterns using the --tile parameter works great on notebooks. Test out different styles and background when generating the pattern. Then use https://www.pycheung.com/checker/ to check and download a larger version of the pattern. Not only can it be used for notebooks, it also works great for digital paper, apparels, mugs and other products.
Funny birthday cards are popular on Etsy. Here I created a birthday card design that can be used as an editable template, or you can help them edit and use a POD service to send them a physical card.
Generate images with a clear subject with a white background. Then remove the background. Finally use websites like Canva to add extra text and graphics.
Similar to the birthday card example above, I created this capybara couple graphic to add to an editable template.
Some words you can use for generating logo designs include: minimalist line logo, emblem logo, simple logo, flat icon. And don't forget to add white background to the prompt so that you can easily removing the background afterwards.
You can create stock photos from Midjourney. See chapter 4 for more details in creating photo realistic images. If you want to make your photos into mockup photos, you can check out this Youtube video but it's quite technical.
Other than the examples above, you can also consider creating other products including: