This is Dallas from the Social Care team here at Shopify.
For dropshipping suppliers, there isn't a way to search by image, but they all have a search navigation bar that you can use to type what you are looking for.
Do you have a dropshipping supplier that you're looking to use? A common one to use is Oberlo as it has a good connection with AliExpress and has a very large catalog to choose from. If you're looking for clothes I suggest you look into Modalyst. It has a great selection of clothing items and a large variety so that is worth looking over in addition to Oberlo. Spocket is another dropshipping supplier with a large selection of a variety of different items.
I'd be happy to try and find a supplier that might be more relevant for what you're wanting to sell, but in order to do that, I'll just need a bit of a clearer idea of what it is that you'd like to sell. Do you have a general idea of what you'd like to do yet or are you still narrowing down your niche?
Please feel free to share more information as I would love to assist you in more detail.