Besides the option of importing your 3D object in various formats described here, now you can also import an object just from an image!
Here's how you can convert your image to 3D:
Open the project you're working on;
In the lower-left corner you can find an icon 'Import 3D':
Click it and then choose Convert image to 3D:
In the next window, check the examples and click Select Image:
Once it's uploaded, you can apply textures, set the default size and a position of the object:
You will be asked to review everything before you submit your 3D model.
Hit 'Submit' to add it to your catalogue. This model is now available for all your projects in the 'My items' list