If you select the image on the Timeline and press the "T" key, it will auto add the last used transition to both the beginning and end of that clip. You can also select multiple clips (control + click, or click and drag to select multiple clips on timeline) and use the same "T" key to apply transitions to all selected.
Hope this might save you some time.
PS... Thanks for the shortcut 'T'! I didn't know this and find it very useful.
We want to thank you for your patience while we worked to make fading your images more streamlined. We are pleased to announce that we have just released our newest, most powerful version of Camtasia yet. With our new Behaviors, you can do lots of things to any kind of images or videos you bring into Camtasia, including Fade.
You can buy Camtasia here or download the trial here.
Please feel free to post your feedback and feature requests here in our Community forums and remember, all technical support-related inquiries should be directed to our dedicated Technical Support team at https://support.techsmith.com/
Senior Software Engineer