Public domain images and image with free-to-use rights attached can be found in various places:
Government Image Sources
Here are some sites to get you started:
Knox Logos
If you are branding your poster with Knox logos, you need to be familiar with the following guidelines:
Knox Graphic Identities Standards
Download Knox Logos, Letterheads, & More
In-Class use of Images & Logos - Copyright Concerns
If you plan to use images including photographs, graphics, corporate logos, etc. within an in-class PowerPoint presentation or on a poster that will be viewed on campus, give credit to the creator of the photograph, graphic, logo, etc. within your work. To make sure you are not violating any copyright restrictions, we recommend you focus on images that have Creative Common licenses. Or try to use government images, they usually fall in the public domain and are free from copyright.
If images aren't free from copyright, you should ask permission from the source prior to use.
If a student, make sure you also aren't accidentally violating the honor code. For more copyright information, visit other pages within the library's Copyright Guide.
Outside-of-Class (conference, webinar, etc.) use of Images & Logos - Copyright Concerns
When using images and logos outside the classroom, whether within a PowerPoint presentation, on a poster, within a webinar, or within another medium, be cautious about copyright restrictions.
Presentations or posters displayed at external conferences, public forums, venues off-campus, etc. can be subject to different fair use or non-profit educational purpose standards than presentations or posters displayed within university classrooms, to those only enrolled within a Blackboard course, etc. Make sure you are vigilant about having appropriate copyright permission for the use of your work. When in doubt, ask the owner, author, source, etc. for permission to use their work.
If a student, make sure you also aren't accidentally violating the honor code. For more copyright information, visit other pages within the library's Copyright Guide.
Image Resolution and Print Size
There is an inverse relationship between print size and resolution (if you increase the print size the resolution decreases and vice-versa).
To get good results when inserting an image into a research poster, the image should be printed at a resolution of at least 120 pixels per inch (ppi).
Images that look good online may not be high enough resolution to look good in print at the size you want them to be.
Watch the video below to see these concepts in action (click to view):
Free Tools for Creating Graphics & Visualizing Data