This is a guide to build a model of hand-sample sized objects (i.e. objects you can carry in your hand) using the process of structure from motion photogrammetry. I've done a few in my day, and thought I'd share a few pearls of wisdom about what I found works well by demonstrating a project I have worked on recently. This guide does assume that you have some familiarity with the software Agisoft Metashape, however, I believe that the software is very well designed and if you take the time to understand the basic principles, you should be able to follow along.
One general note on creating models of objects, before going on with the detail. There are a lot of automatic model generating using tools that are either expensive or use a proprietary process that is difficult to adapt to your use case. I've tried a lot of them, and have always found that they come short of the detail that I need from the sample I'm trying to model. By using the process described in the following steps, you are only limited by the quality of the photos you can take with your camera. Often times, the resulting model quality is better than what you can see with the naked eye! Given this, the two limiting factors are the camera you have at your disposal, and your skill at taking photos.
All right, here are the steps to follow: