Are you talking about a picture file when you are referring to "image"?
If so, then yes, when you convert to another format the malware part will be removed.
The reason for that is because the malicious code is usually hidden in the non-visible part of the picture/image file, such as the header or the footer. Conversion to another format works to remove this malicious code because it will only convert the image part of the JPEG, leaving the malicious code behind when it moves the image to the Bitmap format for example.
Anyway malicious images depends on exploits to execute malicious code, it isnt something simple.