The purpose of this project is to find the smallest image file in various formats, which you can easily use as the default src value in the page before the img loads:
<img src="data:image/jxl;base64,/wr6HwGRCAYBAFAASzhB5k11/Ia1kyog0AHeH0nCAVw">Feel free to commit the smaller size files :)
AAAAHGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZgAAAOptZXRhAAAAAAAAACFoZGxyAAAAAAAAAABwaWN0AAAAAAAAAAAAAAAAAAAAAA5waXRtAAAAAAABAAAAImlsb2MAAAAAREAAAQABAAAAAAEOAAEAAAAAAAAAEgAAACNpaW5mAAAAAAABAAAAFWluZmUCAAAAAAEAAGF2MDEAAAAAamlwcnAAAABLaXBjbwAAABNjb2xybmNseAABAA0ABoAAAAAMYXYxQ4EgAgAAAAAUaXNwZQAAAAAAAAABAAAAAQAAABBwaXhpAAAAAAMICAgAAAAXaXBtYQAAAAAAAAABAAEEAYIDBAAAABptZGF0EgAKBzgABhAQ0GkyBRAAAAtA
Length: 288 bytes.
I created a 1x1 grey image using gimp and got this 288 bytes "nearly lossless" avif, I think it's the smallest.
R0lGODdhAQABAIABAICAgP///ywAAAAAAQABAAACAkQBADs
Length: 35 bytes.
/9j/4AAQSkZJRgABAQEASABIAAD/2wBDAP//////////////////////////////////////////////////////////////////////////////////////wgALCAABAAEBAREA/8QAFBABAAAAAAAAAAAAAAAAAAAAAP/aAAgBAQABPxA
Length: 134 bytes.
From: stackoverflow
/wr6HwGRCAYBAFAASzhB5k11/Ia1kyog0AHeH0nCAVw
Length: 32 bytes.
From: stackoverflow
iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAAAAAA6fptVAAAACklEQVQI12NoAAAAggCB3UNq9AAAAABJRU5ErkJggg
Length: 67 bytes.
JVBERi0xLg10cmFpbGVyPDwvUm9vdDw8L1BhZ2VzPDwvS2lkc1s8PC9NZWRpYUJveFswIDAgMyAzXT4+XT4+Pj4+Pg
Length: 67 bytes.
pdf is not image file and need to be rendered in an iframe
<iframe src="data:application/pdf,JVBERi0xLg10cmFpbGVyPDwvUm9vdDw8L1BhZ2VzPDwvS2lkc1s8PC9NZWRpYUJveFswIDAgMyAzXT4+XT4+Pj4+Pg">From: stackoverflow
<svg xmlns='http:https://www.w3.org/2000/svg'></svg>Length: 46 bytes.
svg file can get smaller data URI:
<img src="data:image/svg+xml,%3csvg xmlns='http:https://www.w3.org/2000/svg'%3e%3c/svg%3e">UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAdQwAIWsP+BiOh/AAA
Length: 38 bytes.