Images in any form are usually primary sources. This includes photographs, drawings, etchings, posters, screenshots, paintings, murals, and basically anything that's been "captured."
For example, a photograph is a primary sources, since it is original to the moment it was taken. A painting, likewise, is original to the moment it was created. A photograph of a painting also counts as a primary source, for both the image and the original painting.
Old newspapers, diaries, and documents are also primary sources, but since it's difficult to access an original copy of, for example, the Constitution or Van Gogh's Starry Night, photos can be used. The original, photographed item is the primary source even if you're not looking at it in real life. This can get complicated, but a good rule of them is that if you're looking at an image, it counts as a primary source.
Below are some images and a slideshow of a variety of primary sources. Flip through them and you'll get the idea!
'Photograph of Arthur Alfonso Schomburg. Is Hayti decadent?
Issued: 1904. Image and original data from the New York Public Library. No Copyright – United States.'
Schomburg Center for Research in Black Culture
All of the examples in the slideshow below "count" as a primary source.
The slideshow is intended to demonstrate that, though a primary sources must be original and tangible, for student purposes, images are fine. Though these are not the original photograph on photo paper, etching, advertisement, statue, etc., you are welcome to consider them as primary.