When i want to display images in a html code with my Arduino i convert them to URI format which i can then just store in the flash or a sd card its read by all browsers fine, i also recommended making use of the html scaling feature so if you have images that are like 1000px by 1000px resize them to 100px and then use the html code to rescale it back up thus saving loads of memory and data to send.
A super easy way i make an image into a web based URI is upload your image to the web on any server or google then right click the image and open open in a new tab then right click and view source and click the source tab then in the left menu list you will see the image name click that and it will show the base64 code which is the URI code you want. you then just call it like a html link to an image.