When
Your PNG is a logo, icon, or flat silhouette.
Then
Remove its background, trace the intended outline to SVG, and import the SVG into Tinkercad.
Give the imported shape height, set its dimensions, and add a solid backing if it needs to stand on its own.
When
Your PNG uses brightness to describe raised and recessed areas.
Then
Create a height-based STL outside Tinkercad, then import the resulting mesh.
A traced outline cannot preserve the image's different height levels. Inspect the mesh before adding a base or mounting features.
When
You already have an image-derived STL.
Then
Import the STL, check its dimensions, and position it with any additional Tinkercad shapes.
This avoids converting the PNG a second time, although fine mesh details may still be difficult to edit.