There are a few variables that determine the outcome of a photo transfer. The main one is the photo you're using. Some photos will transfer with no problems and others won't transfer well at all no matter what you do.
Here are a few pointers to help with transferring those tough photos:
BeadTool lets you choose what types of beads you're willing to work with. When transferring those tough photos it can be helpful to eliminate certain kinds of beads.
In the Show these types section, uncheck the following:
In the Show these finishes section, uncheck the following:
Sometimes it helps if you lighten or darken your photo before starting your transfer.
Experiment with different transfer settings. If you are new to transferring, check the video here.
If you're still not getting good transfers after playing with the above settings, you may need to re-take the photo or edit the photo in a professional photo editor.