Can we create thumbnails from the images for navigation

I am starting to use your images in my wordpress blogs. However, my theme requires a thumbnail of the image/post for my homepage. The thumbnails are small versions of the images that I use in the post, usually around 100x100 or less in size. Am I allowed to create a thumbnail from your images which will be used strickly for navigation purposes in order to navigate the the post where your full images reside?

Thanks