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Yes, this could be because your form needs to upload all the uploaded files, it also depends on the size of the image, if it is a large image and it are multiple images this will be noticed when submitting the form, you can limit the size of the files that are uploaded, take a look on this guide to do it: http://www.jotform.com/help/33-Changing-the-Upload-Size-Limit.
If you are referring to images that you are showing in your form, then it does not affect the form because these images are loaded as soon as the form is loaded and they are not uploaded when the form is submitted.